PCCode: 138831 FINAL 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

Date: December 30, 2013 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

SUBJECT: CYFLUMETOFEN: Report ofthe Cancer Assessment Review Committee 

PC Code: 138831 

Decision No.: N/A 

Petition No.: N/A 

Risk Assessment Type: Cancer Assessment 

TXR No.: 0056862 

MRID No.: N/A 

DP Barcode: N/ A 

Registration No.: N/A 

Regulatory Action: N/ A 

Case No.: N/A 

CAS No.: 

40 CFR: N/A 

FROM: Kristin Rury, Executive Secretary }(Wt> ~()so ( 0 1::..) 

Cancer Assessment Review Committee 

Health Effects Division (7509P) 

THROUGH: Jess Rowland, Chair ~~ : ~ I . \ n--~ \2-l;lo · 

Karlyn Middleton, Co-Chair ~ f\{i o{ck f--.. JL: 

Cancer Assessment Review Committee 

Health Effects Division (7509P) 

TO: Yung Yang, Toxicologist 

RAB VI, Health Effects Division (7509P) 

Richard Gebken 

Product Manager, Registration Division 

The Cancer Assessment Review Committee met on December 17, 2013 to evaluate the 

carcinogenic potential of cyflumetofen in accordance with the EPA 's Final Guidelines for 

Carcinogen Risk Assessment (March, 2005). Attached please find the final Cancer Assessment 

Document. 

1 
PC Code: 138831 FINAL

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CANCER ASSESSMENT DOCUMENT

EVALUATION OF THE CARCINOGENIC POTENTIAL OF 

Cyflumetofen 

PC 138831 

December 30, 2013 

CANCER ASSESSMENT REVIEW COMMITTEE 

HEALTH EFFECTS DIVISION 

OFFICE OF PESTICIDE PROGRAMS 
PC Code: 138831 FINAL

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CONTENTS 

Executive Summary .........................................................................................................................4 

I. Introduction ................................................................................................................................6 

II. Background Information ...........................................................................................................6 

III. Evaluation of Carcinogenicity .................................................................................................6 

1. Combined Chronic Toxicity & Carcinogenicity Study in Fischer 344 Rats ...................6 

2. Carcinogenicity Study in CD-1 Mice ............................................................................12 

IV. Toxicology .............................................................................................................................14 

1. Metabolism ....................................................................................................................14 

2. Mutagenicity ..................................................................................................................15 

3. Structure Activity Relationship ......................................................................................19 

4. Subchronic and Chronic Toxicity ..................................................................................19 

V. Committee’s Assessment of the Weight-of-the Evidence ......................................................23 

1. Carcinogenicity ..............................................................................................................23 

2. Mutagenicity ..................................................................................................................24 

3. Structure Activity Relationship ......................................................................................24 

VI. Classification of Carcinogenic Potential ...............................................................................24

VII. Quantification of Carcinogenicity ..........................................................................................24 

VIII. Bibliography ..........................................................................................................................25 
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EXECUTIVE SUMMARY 

The carcinogenic potential of cyflumetofen was evaluated following dietary administration to 

male and female Fischer 344 rats and male and female CD-1 mice. Two separate studies were 

conducted in both species. In 2004, the Registrant conducted a carcinogenicity study in Fischer 

344 rats (MRID No. 48542697) and a carcinogenicity study in CD-1 mice (MRID No. 48542698). 

Since there was no evidence of carcinogenicity in either species, and to address concern regarding 

the adequacy of the doses tested in the above studies, the Registrant elected to conduct 

supplemental studies to evaluate higher doses in mice (MRID No 49209101) and rats (MRID No. 

49226601). 

Cyflumetofen was administered in the diet to groups of 50 rats/sex/dose for 104 weeks. One study 

was conducted at doses of 0, 150, 500 and 1500 ppm (0, 4.9, 16.5, and 49.5 mg/kg/day in males 

and 6.14, 20.3, and 61.9 mg/kg/day in females) while a second high dose study was conducted at 0 

and 6000 ppm (0 and 220 mg/kg/day in males and 0 and 287 mg/kg/day in females). There was 

limited evidence of carcinogenicity characterized by the presence of thyroid c-cell tumors and 

interstitial cell tumors of the testes in male rats only at the highest dose tested (HDT). There was 

no evidence of carcinogenicity in female rats at any dose level. The doses tested in the rat study 

were considered to be adequate to assess the carcinogenic potential of cyflumetofen. 

The thyroid c-cell tumors were determined to be treatment-related based on the following 

considerations: a statistically significant trend and a pair-wise significance (both at p < 0.05) for 

thyroid c-cell adenocarcinomas when compared to controls; a statistically significant trend (p < 

0.05) and a pair-wise significance (p<0.01) for thyroid c-cell adenomas and/or adenocarcinomas 

combined; and the incidences of the adenocarcinomas (31%) and the combined tumors (57%) 

exceeded the historical control range from the testing laboratory (c-cell adenocarcinoma, 6-18%, 

and combined c-cell adenoma/carcinomas, 26-50%). 

The testicular interstitial cell tumors, although exacerbated by treatment were not considered to be 

biologically relevant since this tumor (Leydig cell, LCT) is extremely common in the F344 rat, 

with a reported background incidence of 56-100% in 2-year cancer studies. The reasons for the 

different background incidence rate for LCT among species stem from both quantitative and 

qualitative differences in the Leydig cell response to hormonal stimuli. The rat Leydig cell is 

extremely sensitive to slight changes in circulating luteinizing hormone (LH) levels. Among rat 

strains, the F344 rat is particularly susceptible to this process and is not considered a relevant 

model for studying LCT. By contrast, the incidence rate in humans of LCT is very low (i.e., 

0.00004%). Similarly, rats are known to have approximately 13-times more LH receptors per cell 

than humans (Hutaniemi, 1983). Because of the differences present between the human and the rat 

Leydig cells, non-genotoxic compounds that cause LCTs in rats have little relevance to humans. 

The data with cyflumetofen supports this species and strain-specific effect on the Leydig cells. 
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The carcinogenic potential of cyflumetofen was evaluated following dietary administration to 

male and female CD-1 mice. Two studies were conducted in the mice. Cyflumetofen was 

administered to groups of 52 mice/sex/dose for 78 weeks. One study was conducted at doses of 0, 

150, 500, 1500 and 5000 ppm (0, 15.5, 54.3, 156 and 537mg/kg/day in males and 14.3, 48.1, 144 

and 483 mg/kg/day in females) while a second high dose study was conducted at 0 and 10,000 ppm 

(0 and 1143 mg/kg/day in males and 1132 mg/kg/day in females. There was no evidence of 

carcinogenicity in male or female mice at any dose level. The doses tested in the mouse were 

considered adequate to assess the carcinogenic potential of cyflumetofen.

The mutagenic potential of cyflumetofen, its metabolites, and an impurity was tested in in vitro

and in vivo studies. There was no concern for mutagenicity for the parent, the metabolites or the 

impurity. Consequently, mutagenicity can be ruled out as a possible mode of action for tumor 

formation. 

In accordance with the EPA's Final Guidelines for Carcinogen Risk Assessment (March, 2005), 

the Cancer Assessment Review Committee (CARC) classified cyflumetofen as “Suggestive 

Evidence of Carcinogenic Potential”. This classification is based on the presence of a single tumor 

type (thyroid c-cell) in one sex (male) and one species (rat), and the lack of concern for 

mutagenicity. When there is suggestive evidence of carcinogenicity, the Agency does not attempt 

a dose-response assessment as the nature of the data generally would not support one. Therefore, 

the Agency has determined that quantification of risk using a non-linear approach (i.e. the chronic 

reference dose) will adequately protect for all chronic toxicity, including carcinogenicity, likely to 

result from exposure to cyflumetofen. 
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I. INTRODUCTION

On December 17, 2013, the Cancer Assessment Review Committee (CARC) of the Health Effects 

Division of the Office of Pesticides Program met to evaluate the carcinogenic potential of 

cyflumetofen. Dr. Yung Yang, RAB VI, presented the chronic toxicity/carcinogenicity study in 

Fischer 344 rats and the carcinogenicity study in CD-1 mice. 

II. BACKGROUND INFORMATION 

Cyflumetofen (PC 138831; CAS# 400882-07-7) is a new active ingredient that belongs to the 

acrylonitrile class of chemicals with a novel insecticidal mode of action – mitochondria complex II 

electron transport inhibition. It is a selective contact miticide that is effective on all mite life stages. 

It is currently proposed only for foliar applications via ground or aerial equipment. 

The toxicology database is complete for cyflumetofen. The major target organ in rats, mice, and 

dogs following short- and long-term oral administration of cyflumetofen is the adrenal glands 

characterized by increased organ weight and histopathology (vacuolation and hypertrophy of the 

adrenal cortical cells). Cyflumetofen has low acute toxicity (acute lethality studies) by oral, dermal, 

and inhalation routes of exposure. It is minimally irritating to the eyes but not to the skin. It is a 

skin sensitizer. 

The toxicity database contains two sets of carcinogenicity studies in mice and rats. In 2004, the 

Registrant conducted a carcinogenicity study in Fischer 344 rats (IET 01-0125) and a 

carcinogenicity study in CD-1 mice (IET 02-0039). Since there was no evidence of 

carcinogenicity in either species, and to address the adequacy of doses tested in the above studies, 

the Registrant elected to conduct supplemental studies at higher doses in mice and rats. This 

CARC evaluation includes discussion of these four studies. 

III. EVALUATION OF CARCINOGENICITY STUDIES

1. Combined chronic toxicity/carcinogenicity Study in F-344 Rats

References: 

1. 2004: Carcinogenicity Study in Rats. The Institute of Environmental Toxicology, Ibaraki, 

Japan. Laboratory report number: IET 01-0125. Study report date: 29-July-2004. 

Applicant Report Number: OSTA-0046(EN)-FR. DACO 4.4.2. MRID 48542697.

2. 2013: Carcinogenicity Study in Rats. Institute of Environmental Toxicology; Mitsukaido 

Ibaraki, Japan. Laboratory report number: IET; Study report Number: 11-0002; Report 

date: 07-Oct-2001. MRID 49226601
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A. Experimental Design

In the 2004 carcinogenicity study (MRID 48542697), cyflumetofen (OK-5101, 97.67 % a.i.) was 

administered to Fischer 344 rats (50/sex/dose) in the diet at dose levels of 0, 150, 500, or 1500 ppm 

(0, 4.92/6.14, 16.5/20.3, and 49.5/61.9 mg/kg bw/day in males/females) for 104 weeks.

In the 2013 supplementary carcinogenicity study (MRID 49226601), cyflumetofen was 

administered in the feed to F344 rats (50/sex/dose) at doses of 0 or 6000 ppm (0, 220/287 mg/kg 

bw/d in males/females) for 104 weeks. 

B. Survival Analysis

There were no statistically significant survival disparities among the dose groups for male rats in 

either the 2004 or the 2013 study or in the two studies combined (Table 1). Because of the lack of 

survival disparities, the two studies have been combined for more robust statistical tumor analyses. 

Table 1. Mortality Rates in F344 Rats Fed Cyflumetofen for 2 years 

Cox or Generalized K/W Test Results for the Combined Studies (2004 and 2013) 

Dose (ppm) Weeks: 1-26 Weeks: 27-52 Weeks: 53-78 Weeks 

79-105f

Total

0 0/100 1/100 2/99 14/97 17/100 

(17)

150 0/50 0/50 2/50 8/48 10/50 

(20)

500 0/50 0/50 2/50 6/48 8/50

(16)

1500 0/50 0/50 2/50 7/48 9/50 

(18)

6000 0/50 0/50 0/50 7/50 7/50 

(14)

+Number of animals that died during the interval/Number of animals alive at the beginning of the interval. 

f

Final sacrifice at week 105. 

( ) Percent. 
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C. Discussion of Tumor Data

Tumors of the thyroid glands and the testes were seen in male rats only. There were no 

treatment-related tumors in female rats. The statistical analyses of these tumors in the male rats 

were based upon the Exact test for trend and the Fisher’s Exact Test. 

Thyroid tumors: As shown in Table 2, there was a statistically significant trend, and a pair-wise 

significance at the high dose (both at p < 0.05) for thyroid C-cell adenocarcinomas when compared 

to controls. There was also a statistically significant trend (p < 0.05) and a pair-wise significance 

(p<0.01) for thyroid c-cell adenomas and/or adenocarcinomas combined at the low (150 ppm) and 

high (6000 ppm) dose groups. It is to be noted that animals in the 150 and 500 ppm dose groups 

only received microscopic evaluations of the thyroid if gross lesions were palpated. At the high 

dose, the incidences of adenomas (31%) were within the historical control range (20-44%) of the 

testing laboratory; whereas, the incidences of adenocarcinomas (31%) and the combined tumors 

(57%) exceeded the historical control range (c-cell adenocarcinoma, 6-18%), and combined c-cell 

adenoma/carcinomas, 26-50%). 

Table 2. Incidences of Thyroid C-Cell Tumor Rats in F344 Rats Fed Cyflumetofen 

Fisher’s Exact and Exact Trend Test Results for the Combined Studies (2004 and 2013) 

 0 ppm 150 ppm 500 ppm 1500 ppm 6000 ppm 

Adenomas 

 (%) 

p = 

20/99 

(20) 

0.1457 

8a/23 

(35) 

0.1128 

4/15 

(27) 

0.3903 

11/50 

(22) 

0.4779 

15/49 

(31) 

0.1164 

Adenocarcinomas 

(%) 

p = 

15/99 

(15) 

0.0214* 

7/23 

(30) 

0.0826 

2/15 

(13) 

0.6977 

4/50 

(8) 

0.9375 

15b/49 

(31) 

0.0253* 

Combined 

(%) 

p = 

33c/99 

(33) 

0.0123* 

15/23 

(65) 

0.0052** 

6/15 

(40) 

0.4066 

14d/50 

(28) 

0.8011 

28e/49 

(57) 

0.0049** 

+Number of tumor bearing animals/Number of animals examined, excluding those that died before week 52. 

#Animals in the 150 and 500 ppm dose groups only received microscopic evaluations of the thyroid if gross lesions 

were palpated. 

a

First Adenoma observed at week 98, dose 150 ppm 

b

First Adenocarcinoma observed at week 94, dose 6000 ppm 

c

Two animals in the control group had both an adenoma and an adenocarcinoma. 

d

One animal in the 1500 ppm dose group had both an adenoma and an adenocarcinoma. 

e

Two animals in the 6000 ppm dose group had both an adenoma and an adenocarcinoma. 

Note: Significance of trend denoted at control. 

 Significance of pair-wise comparison with control denoted at dose level. 

 If *, then p < 0.05. If **, then p < 0.01. 
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Table 3. Historical Control Data for Thyroid C-cell Tumors at Testing (IET) Laboratorya 

Organs and lesions 

Study ID A B C D E F G H I

b

Year 1997 1997 1998 1998 1998 1998 1999 2003 2003

N 50 50 50 50 50 50 50 50 50 

Thyroid: 

Adenoma, C-cell 8 8 20 13 8 14 12 9 9 

 (%) (16) (16) (40) (26) (16) (28) (24) (18) (18) 

Carcinoma, C-cell 0 0 2 4 0 4 2 5 6 

 (%) (0) (0) (4) (8) (0) (8) (4) (10) (12) 

Organs and lesions 

Study ID J K L M N O P 

Year 2005 2005 2008 2009 2009 2011 2012

N 50 50 50 50 50 50 50 

Thyroid: 

Hyperplasia, C-cell 

(%) 

-- 

-- 

15 

(30) 

20 

(40) 

9 

(18) 

19 

(38) 

23 

(46) 

35 

(70) 

Adenoma, C-cell 16 20 21 22 10 14 18 

 (%) (32) (40) (42) (44) (20) (28) (36) 

Carcinoma, C-cell 3 2 7 3 5 9 7 

(%) (6) (4) (14) (6) (10) (18) (14) 

C-cell Adenoma/carcinoma 

(combined) (%) 

19 

(38) 

22 

(44) 

25 

(50) 

25 

(50) 

13 

(26) 

20 

(40) 

21 

(42) 

a Taken from page 45 of the study report and additional data submitted by the applicant 

b

 Control data from the original 2-year rat carcinogenicity study (PMRA 2146822, MRID 48542697) 

Testicular tumors: As shown in Table 4, for the interstitial cell tumors, there was a significant 

trend (p < 0.01), and a pair-wise significance (p < 0.05) at the high dose (6000 ppm) when 

compared to controls. However, the incidences of interstitial cell tumors in the current study (82 to 

96%) were within the testing laboratories historical control range (56 – 100%). It should be noted 

that there is a high background rate for this tumor type in the particular strain of rat (Fischer344) 

tested. By contrast,, the incidence rate in humans of LCT is very low (i.e., 0.00004%). Similarly, 

rats are known to have approximately 13-times more LH receptors per cell than humans 

(Hutaniemi, 1983). Also, there was no corroborative increase in non-neoplastic lesions of the 

testes at the high dose. In fact, there was a decrease in the incidence of interstitial cell hyperplasia 

at the high dose (3/50; 6%) when compared to controls (19/50; 28%). Consequently, the 

observance of this tumor type is of questionable biological significance/relevance 
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Table 4. Incidence of Testicular Tumors in F344 Rats Fed Cyflumetofen 

Fisher’s Exact and Exact Trend Test Results for the Combined (2004 & 2013) Studies 

 0 ppm 150 ppm 500 ppm 1500 ppm 6000 ppm 

Interstitial Cell Tumors 

 (%) 

p = 

81/99 

(82) 

0.00565** 

42/48 

(88) 

0.38475 

43a/48 

(90) 

0.16556 

46/50 

(92) 

0.07560 

48/50 

(96) 

0.01163* 

+Number of tumor bearing animals/Number of animals examined, excluding those that died before week 52. a

First Interstitial Cell Tumor observed at week 77, dose 500 ppm. 

Note: Significance of trend denoted at control. 

 Significance of pair-wise comparison with control denoted at dose level. 

 If *

, then p < 0.05. If **, then p < 0.01. 

Table 5. Historical Control Data for Interstitial Cell Tumors at Testing (IET) Laboratory 

(1993-2012) 

Study Year

1993 1994 1995 1997 1998 1999 2003 2005 2008 2009 2011 2012

Study 1 43/50

86%

42/50

84%

43/50

86%

49/50

98%

39/50

78%

35/50

70%

43/50

86%

42/50

84%

36/50

72%

31/50

62%

28/50

56%

36/50

72%

Study 2 42/50

84%

48/50

96%

42/50

84%

48/50

96%

40/50

80%

43/50

86%

41/50

82% 

Study 3 44/50

88%

46/50

92% 39/50

78% 

Study 4 50/50

100% 34/50

68% 

Year: Year at termination of treatment. 

C. Non-Neoplastic Lesions

In the 2004 study (MRID48542697), An increased incidence of diffuse hypertrophy and 

hyperplasia of adrenal cortical cells was noted in high dose males and females after 

histopathological examination (Table 6). This finding correlates with the increased adrenal 

weights at this dose level. In addition, an increased incidence of luminal dilatation of the gland in 

the uterine horn was observed in mid and high dose females. Both of these findings were 

considered to be treatment related. High dose males exhibited a decreased incidence of atrophy of 

the seminiferous tubules and interstitial cell hyperplasia in the testis. Since the change was a 

decrease, these observations were not considered toxicologically relevant. No biologically 

relevant non-neoplastic lesions in the thyroid were observed. 
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Table 6. Incidence of Selected Non-Neoplastic Lesions (all animals) in Rats Fed Cyflumetofen 

(2004 study) 

Males (ppm)

Organ and lesions 0 150 500 1500

Adrenal 

 cortical cell hypertrophy (diffuse)

 cortical cell hyperplasia

N=50

4

13

N=50

2

7

N=50

4

10

N=50 

16**

17

Thyroid

 Hyperplasia C-cell 

N=42

19

N=13a

1

N=7a

1

N=41 

15

Testis

 Atrophy, seminiferous tubule

 Hyperplasia, interstitial cell

N=42

0

18

N=39a

6

9

N=41a

4

13

N=41

2

7

Females (ppm)

Organ and lesions 0 150 500 1500

Adrenal 

 cortical cell hypertrophy (diffuse)

 cortical cell hyperplasia

Uterine horn gland luminal dilatation

N=50

3

16

6

N=50

3

15

7

N=50

1

14

12

N=50 

23**

23

 14**

Thyroid

 Hyperplasia C-cell 

N=43

12

N=10a

2

N=4a

1

 N=45

8

** Significantly different from control, p<0.01 

a Examined on the animals that showed macroscopic lesions. 

In the 2013 supplementary carcinogenicity study (MRID 49226601), histopathological 

examination revealed an increased incidence of diffuse hypertrophy and focal vacuolation of 

adrenal cortical cells in treated males and females (Table 7). In addition, treated females also 

exhibited an increased incidence of diffuse adrenal cortical cell vacuolation. These findings 

correlate with the increased adrenal weights observed in treated animals of both sexes. Treated 

males also exhibited an increased incidence of focal atrophy of the acinar cells in the pancreas. 

Although the incidence was within the range of reported historical control data values (7/50 – 

36/50 for years 2008-2012), this lesion was also observed in treated males in the 1-year rat chronic 

toxicity study (MRID 49029701) at the same dose level (6000 ppm) and was therefore determined 

to be related to treatment. While the incidence of atrophy of the seminiferous tubules and 

hyperplasia of the interstitial cells of the testis were statistically significantly decreased, these 

changes were considered to be secondary effects to the development of testicular interstitial cell 

tumors. 
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Table 7: Incidence of Selected Non-Neoplastic Lesions (all animals) in Rats Fed Cyflumetofen 

 (2013 Study) 

Organ / Lesion

Dose Group (ppm)

Male Female

0 6000 0 6000

N=50 N=50 N=50 N=50

Testis: 

Atrophy, seminiferous tubule 27/50 5/50** - -

Hyperplasia, interstitial cell 19/50 3/50** - -

Pancreas:

Atrophy, acinar cell, focal 15/50 27/50* 5/50 2/50

Thyroid: 

Hyperplasia, C-Cell 17/50 18/50 16/49 14/50

Adrenal:

Hypertrophy, cortical cell, diffuse 7/50 44/50** 5/50 39/50**

Vacuolation, cortical cell, diffuse 12/50 7/50 3/50 23/50**

Vacuolation, cortical cell, focal 6/50 15/50* 12/50 24/50**

Fisher's exact probability test: **P<0.01; * P<0.05. 

D. Adequacy of the Dosing for Assessment of Carcinogenicity

The doses tested were considered to be adequate to assess the carcinogenic potential of 

cyflumetofen based on effects on clinical signs of toxicity (females), decreased body weight (both 

sexes) and body weight gain (males), changes in hematological parameters (males), organ weights 

(both sexes), histopathology findings (both sexes), and tumor formations at the high dose (6000 

ppm) in the supplemental study. 

2. Carcinogenicity Study in CD-1 Mice

References: 

1. 2004: Carcinogenicity Study in Mice. The Institute of Environmental Toxicology, Ibaraki, 

Japan. Laboratory report number: IET 02-0039. Study report date: 27-July-2004. 

Report Number: OTSA-0061 (EN)-FR. DACO 4.4.3. (MRID 48542698) 

2. 2013: BAS 9210 I (Cyflumetofen): Carcinogenicity Study in Mice. The Institute of 

Environmental Toxicology, Ibaraki, Japan. Laboratory report number: IET 11-0016. 

Study report date: 08-August-2013. Report Number: 2013/1251154. DACO 4.4.3. 

(MRID 49209101) 
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A. Experimental Design

In the 2004 carcinogenicity study (MRID 48542698), cyflumetofen (OK-5101, 97.67 % a.i.) was 

administered to CD-1 mice (52/sex/dose) in the diet at dose levels of 0, 150, 500, 1500 or 5000

ppm (0, 15.5/14.3, 54.3/48.1, 156/144, and 537/483 mg/kg/day in males/females) for 78 weeks. 

In the 2013 supplementary carcinogenicity study (MRID 4920910), cyflumetofen (OK-5101, 

97.82 % a.i.) was administered to SPF ICR (Crj:CD1) mice (52/sex/dose) in the diet at dose levels 

of 0 and 10,000 ppm (0 and1143/1132 mg/kg bw/day in males/females) for 78 weeks. 

B. Discussion of Tumor Data

There was no treatment-related increase in any tumor type in either sex of mice when compared to 

controls. 

C. Non-Neoplastic Lesions

In the 2004 carcinogenicity study (MRID 48542698), histopathological examination noted an 

increased incidence of diffuse adrenal cortical cell vacuolation in males and females of the 5000 

ppm dose group (Table 8). This finding was considered to be treatment related due to a 

corresponding increase in adrenal weight. In addition, an increased incidence of mucosal epithelial 

cell hyperplasia of the glandular stomach in 150 ppm group males was observed. Since this 

increase did not occur in a dose-related manner and there was no corresponding histopathological 

finding at this dose level, this finding was considered not toxicologically relevant. 

Table 8. Incidence of Selected Non-Neoplastic Lesions (all animals) in Mice Fed Cyflumetofen 

Males (ppm)

Organ and lesions 0

n = 52

150

n = 52

500

n = 52

1500

n = 52

5000

n = 52

Adrenal cortical cell vacuolation (diffuse) 1 3 2 3 8*

Females (ppm)

Organ and lesions 0

n = 52

150

n = 52

500

n = 52

1500

n = 52

5000

n = 52

Adrenal cortical cell vacuolation (diffuse) 7 4 4 9 26**

* Significantly different from control, p<0.05 

** Significantly different from control, p<0.01 
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In the 2013 supplementary carcinogenicity study (MRID 49209101), histopathological 

examination revealed an increased incidence of diffuse adrenal cortical cell vacuolation and 

deposition of brown pigment in the cortico-medullary junction in treated males and females (Table 

9). These findings were considered to be treatment-related due the magnitude of the increase in 

both sexes and the corresponding increase in adrenal weight in females. In addition, an increased 

incidence of extramedullary hematopoiesis was observed in the spleen of treated females. 

Table 9. Incidence of Selected Non-Neoplastic Lesions (all animals) in Mice Fed Cyflumetofen

0 mg/kg/day 1143 mg/kg/day

Males (52/dose)

Adrenal cortical cell vacuolation (diffuse) 0 21**

Brown pigment deposition, cortico-medullary junction 6 14**

0 mg/kg/day 1132 mg/kg/day

Females (52/dose)

Adrenal cortical cell vacuolation (diffuse) 2 41**

Brown pigment deposition, cortico-medullary junction 27 44** a

 Data obtained from page 140 in the study report 

* Significantly different from control, p<0.05 

** Significantly different from control, p<0.01 

D. Adequacy of Dosing for Assessment of Carcinogenicity

The dose tested in the supplementary study was the Limit Dose (10,000 ppm or 1000 mg/kg/day) 

and was considered to be adequate to assess carcinogenicity of cyflumetofen in mice. 

Treatment-related findings at this dose included: clinical signs of toxicity, increased adrenal 

weights, enlarged spleen, increased incidence of extramedularry hematopoiesis in the spleen of 

treated females, increased incidence of diffuse adrenal cortical cell vacuolation, and deposition of 

brown pigment in the cortico-medullary junction of the adrenals in both sexes. 

IV. TOXICOLOGY

1. Metabolism 

There were a series of metabolism studies conducted for cyflumetofen. 14C-cyflumetofen was 

rapidly absorbed following administration of the low dose, with plasma levels of radioactivity 

peaking at 1 hour post-dosing. Absorption was slightly slower following administration of the 

high dose, with peak plasma levels attained at 2-4 hours post-dosing indicating saturation of 

absorption. At the high dose, females demonstrated higher Cmax and area under the curve (AUC) 

values than males. 

At 72 hours post-dosing, the gastrointestinal tract, carcass, liver and kidney contained the highest 
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proportions of radioactivity. Most of the radioactivity excreted in urine from low dose rats 

(90-96%) was eliminated within 24 hours after dosing, whereas at the high dose, excretion was 

slower with only 74-88% eliminated within 24 hours of dosing. At both low and high doses, 

60-89% of the radioactivity excreted in feces was eliminated within 24 hours of dosing. 

The unchanged parent was not detected in the urine of any test group. Metabolite AB-3 was 

identified as a major metabolite in the urine of female rats but was a minor urinary metabolite in 

males. Metabolite AB-2 was a minor metabolite in urine of all test groups except females from the 

low dose group, in which residues for this metabolite reached 4% of the administered dose. 

The major metabolites detected in the bile from all test groups were the glucuronic acid conjugates 

of metabolites AB-1 and AB-3. Metabolite AB-2 was also detected at lower levels in the bile 

from all test groups. Unique metabolites identified in the bile of rats administered the A-ring or 

B-ring label included the glucuronic acid conjugate of A-6 and the glutathione conjugate of B-1, 

respectively. 

14C-cyflumetofen was metabolized in the rat primarily by hydrolytic cleavage of the 

trifluoromethylbenzoyl moiety resulting in metabolite B-1 (trifluoromethylbenzoic acid) and A-18. 

Another minor pathway included successive hydroxylation of the tert-butyl side chain. 

2. Mutagenicity: 

Cyflumetofen, two metabolites (B-1 and B-3) and one impurity (AB-13) were evaluated in a 

comprehensive battery of Genetic Toxicology assays. The data indicate that neither the parent 

compound nor metabolite B-1 were mutagenic in bacteria. However, metabolite B-3 induced a 

weak but reproducible and concentration-related mutagenic response (1.7- 2.2 fold increases at 

3330 and 5000 μg/plate) in Salmonella typhimurium TA100; the effect was, nevertheless, 

abolished in the presence of exogenous metabolic activation. There was also evidence of a 

mutagenic response in the L5178Y mouse lymphoma assay that was induced by the parent and the 

two metabolites. The response was the strongest in the parent compound (90 μg/mL –S9 vs. the 

limit concentration for the two metabolites). However, for both the parent and metabolite B-1, 

mutagenic activity was only seen at severely cytotoxic concentration (i.e., ≈10% survival); 

consequently, these results are not considered sufficient evidence of a mutagenic response in this 

test system. For metabolite B-3, the 4.3-fold increase in the mutation frequency at 1891 μg/mL 

(equivalent to the limit concentration of 10 mM) was confined to this level and not observed in the 

S9-activated portion of the assay. 

For the remaining genetic endpoints, the parent and the two metabolites were not clastogenic in 

Chinese hamster lung cells (parent in two studies performed by independent laboratories) or 

peripheral human lymphocytes (metabolites B-1 and B-3). Similarly, cyflumetofen was not 

clastogenic or aneugenic in mouse bone marrow cells up to the limit dose. Finally, neither the 

parent nor the two metabolites induced a genotoxic response in hepatocytes harvest from male rats 

orally exposed up to the limit dose (parent and metabolite B-1) or an overtly toxic level for the test 

animals (metabolite B-3). 
PC Code: 138831 FINAL

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Studies performed on an impurity of cyflumetofen (AB-13) showed negative results for reverse 

gene mutations in bacteria (S. typhimurium TA 1535, TA 1537, TA 98 or TA 100 or Escherichia 

coli WP2 uvrA), forward gene mutations in mammalian cells (L5178Y mouse lymphoma cells), 

and chromosome aberrations in mammalian cells (human peripheral lymphocytes). 

Overall, the data indicate that while there was some evidence of a mutagenic response from in vitro 

assays, the responses were confined to severely cytotoxic concentrations, abolished in the 

presence of exogenous metabolic activation, or were not expressed in whole animal studies. 

Based on these considerations, there is no concern for mutagenicity for the parent or the 

metabolites. Similarly, the impurity was uniformly negative; hence, there is also no concern for 

mutagenicity. All assays were well-conducted, acceptable and satisfy FIFRA test guidelines for 

mutagenicity testing. Consequently, mutagenicity can be ruled out as a possible mode of action 

for tumor formation. Results from these assays are summarized below: 

Parent 

Cyflumetofen was negative in bacteria in two independent trials using the pre-incubation method 

at concentrations of 20.6 to 5000 μg/plate +/-S9 (MRID 48542687). 

In the mouse lymphoma forward gene mutation assay, concentrations of 20 to 90 μg/mL –S9 or 10 

to 140 μg/mL +S9 for 3 hours. Although increases in the total mutation frequencies (MF) 

occurred at 90 μg/mL –S9 (3.2-fold) and at 140 μg/mL +S9 (6.1-fold), these concentrations were 

insoluble and severely cytotoxic (relative suspension growth (RSG) was 10% at 90 μg/mL –S9 and 

12% at 140 μg/mL +S9). These results are, therefore, not considered sufficient evidence of a 

mutagenic response in this test system (MRID 48542692). 

In an in vitro chromosome aberration study, Chinese hamster lung fibroblasts (V79) cells were 

exposed to 6.25 to 50 μg/mL –S9 and 25 to 200 μg/mL +S9 for 6 hours and allowed an 18-hour 

recovery period. Cells were also continuously treated with 3.75 to 30 μg/mL –S9 for 24 or 48 

hours and harvested at the end of treatment. Compound precipitation was seen at ≥200 μg/mL 

+S9. Less than 50% of the cells were available for analysis at the highest dose tested with or 

without S9 activation. There were however, and no significant increases in cells with structural 

or numerical chromosome aberrations (MRID 48542689). 

In a second in vitro chromosome aberration study, Chinese hamster lung fibroblasts (V79) cells 

were exposed to 2.5 to 80 μg/mL –S9 and 10 to 160 μg/mL +S9 for 4 hours and allowed a 14-hour 

recovery period. Due to severe cytotoxicity, the assay was repeated with 3.1 to 10 μg/mL –S9. 

Cells were also continuously treated with 3.1 to 40 μg/mL –S9 for 18 hours and harvested or 

allowed an additional 10 hour recovery. With S9, cells were dosed with 20-320 μg/mL for 4 

hours and harvested after a 24-hour recovery period. Compound precipitation was seen at ≥120 

μg/mL. Less than 50% of the cells were available for analysis at ≥160 μg/mL +S9, ≥20 

μg/mL-S9 (18-hour exposure), or 40 μg/mL-S9 (18-hour exposure with 10-hour recovery). 

There were however, and no significant increases in cells with structural or numerical 

chromosome aberrations (MRID 48542691). 
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In the mouse bone marrow micronucleus assay, levels up to the limit dose were not overtly toxic to 

the test animals, cytotoxic to the target cells or induce an aneugenic or a clastogenic response 

(MRID 48542694). 

In an in vivo unscheduled DNA synthesis (UDS) assay in male Wistar rats, metabolite B-1 was not 

overtly toxic to the test animals or genotoxic in the hepatocytes harvested 2-4 or 12-16 hours after 

oral administration of levels up to the limit dose of 2000 mg/kg (MRID 48542695). 

Metabolite B-1 

Metabolite B-1 was negative in bacteria in two independent trials using the plate incorporation 

method at concentrations of 3 to 5000 μg/plate +/-S9 (MRID 48542710). 

In the mouse lymphoma forward gene mutation assay, concentrations of 1 to 1901 μg/mL +/–S9 

(1901 μg/mL is equivalent to the limit concentration of 10 mM) were tested using a 3-hour 

exposure. A second assay was performed with comparable nonactivated concentrations and a 

24-hour exposure and S9-activated levels of 3-1910 μg/mL with a 3-hour exposure. The 

nonactivated assay was repeated for the 24-hour exposure with 3- 1910 μg/mL. The 3-hour 

exposure with or without S9 activation was negative up to the highest dose tested (HDT). 

Although marked increases in the total MF occurred at the HDT without S9 activation after the 

24-hour treatment in both the initial (8.2-fold) and repeat trials (7-fold), these concentrations were 

severely cytotoxic (RSG was 13 or 9%, respectively). Consequently, these results are not 

considered sufficient evidence of a mutagenic response in this test system (MRID 48542712). 

In an in vitro chromosome aberration study, peripheral human lymphocytes were exposed to 333 

to 1901 μg/mL +/–S9 (1901 μg/mL is equivalent to the limit concentration of 10 mM) for 3 hours 

and allowed a 21-hour recovery period. Cells were also continuously treated with 100 to 1000 

μg/mL –S9 for 24 or 48 hours and harvested at the end of exposure. With S9, cells were dosed 

with 333-1901 μg/mL for 3 hours and harvested after 48 hours. There were no significant increases 

in cells with structural chromosome aberrations without S9 activation up to concentrations that 

caused a ≥50% decrease in relative suspension growth (≥ 750 μg/mL, prolonged 24-hour exposure 

or (≥ 560 μg/mL, prolonged 48-hour exposure). Similarly, no evidence of a clastogenic response 

was seen after exposure for 3 hours with or with S9 up to the limit dose (MRID 48542711). 

In an in vivo unscheduled DNA synthesis (UDS) assay in male Wistar rats, metabolite B-1 was not 

overtly toxic to the test animals or genotoxic in the hepatocytes harvested 2-4 or 12-16 hours after 

oral administration of levels up to the limit dose of 2000 mg/kg (MRID 48542713). 

Metabolite B-3 [2-(trifluoromethyl)benzamide] 

Metabolite-3 induced a reproducible and dose-related increase in mutant colonies of Salmonella 

typhimurium TA100. Fold increases were 1.7 and 1.9-fold at 3330 and 5000 μg/plate –S9 in Trial 

1 and 1.7 and 2.2-fold at 3330 and 5000 μg/plate –S9 in Trial 2. The response was, however, 

abolished in the presence of S9 activation and was not seen in any other Salmonella strain or in 

Escherichia coli WP2 uvrA (MRID 48542715). 
PC Code: 138831 FINAL

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In the mouse lymphoma forward gene mutation assay, concentrations of 1 to 1891 μg/mL +/–S9 

(1891 μg/mL is equivalent to the limit concentration of 10 mM) were tested using a 3-hour 

exposure. A second assay was performed with comparable nonactivated concentrations and a 

24-hour exposure and comparable S9-activated concentrations with a 3-hour exposure. The 

3-hour exposure with or without S9 activation was negative up to the highest dose tested (HDT). 

A marked increase in the total MF occurred at the HDT without S9 activation (4.3-fold) following 

the prolonged and in the absence of severe cytotoxicity. However, the response was confined to 

this concentration and not observed when S9 activation was incorporated into the reaction mixture 

(MRID 48542717). 

In an in vitro chromosome aberration study, peripheral human lymphocytes were exposed to 333 

to 1891 μg/mL +/–S9 (1891 μg/mL is equivalent to the limit concentration of 10 mM) for 3 hours 

and allowed a 21-hour recovery period. Cells were also continuously treated with 100 to 1891 

μg/mL –S9 for 24 hours or 33 to 1891 μg/mL –S9 for 48 hours. Cells were harvested at the end of 

the prolonged exposures. With S9, cells were dosed with 333-1891 μg/mL for 3 hours and 

harvested after 48 hours. There were no significant increases in cells with structural chromosome 

aberrations with or without S9 up to the limit concentrations (MRID 48542716). 

In an in vivo unscheduled DNA synthesis (UDS) assay in male Wistar rats, metabolite B-3 was 

toxic to the test animals at 350 mg/kg but was not genotoxic in the hepatocytes harvested 2-4 or 

12-16 hours after oral administration of 0, 175 or 350 mg/kg (MRID 48542718). 

Impurity AB-13 

Impurity AB-13 was negative in bacteria in two independent trials using the plate incorporation 

method up to insoluble concentrations (≥333 μg/plate +/-S9) (MRID 48542688). 

In the mouse lymphoma forward gene mutation assay, concentrations of 0.03 to 100 μg/mL +/–S9 

were tested using a 3-hour exposure. A second assay was performed with similar concentrations 

and a 24-hour exposure for the nonactivated phase of testing and with a 3-hour exposure for the 

S9-activated concentrations. The 3-hour exposure with or without S9 activation was negative up 

to the highest dose tested. Compound precipitation was seen at 100 μg/mL +/–S9. RSG was 

generally similar to the control at all concentrations and exposure intervals. There was no 

appreciable increase in the MF at any nonactivated or S9-activated concentration (MRID 48849413). 

In an in vitro chromosome aberration study, peripheral human lymphocytes were exposed 

continuously to 10 to 333 μg/mL –S9 for 24 or 48 hours and harvested at the end of the prolonged 

exposures. With S9, cells were dosed with 10 to 333 μg/mL for 3 hours and harvested after 48 

hours. Compound precipitation was noted at ≥100 μg/mL. There were no adverse effects on the 

mitotic indices or significant increases in cells with structural chromosome aberrations with or 

without S9 up to insoluble levels (MRID 48542716690). 
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3. Structure-Activity Relationship 

No structure-activity relationship information is available for cyflumetofen in the OncoLogic 

expert system. 

 4. Subchronic and Chronic Toxicity

a) Subchronic Toxicity in Rats 

In a subchronic toxicity study (MRID 48542682), cyflumetofen (OK-5101, 97.6% a.i.) was 

administered to 10 Fischer rats/sex/dose in the diet at dose levels of 0, 100, 300, 1000 and 3000 

ppm (0, 5.4, 16.5, 54.5 and 167 mg/kg//day in males, 0, 6.28, 19.0, 62.8 and 193 mg/kg bw/day in 

females) for 90 days. 

Indications of liver effects were seen. OK-5101 caused an increase in prothrombin time in high 

dose males. In females, increases observed in albumin/globulin ratio in the 1000 and 3000 ppm 

groups were correlated to the decreases in observed globulin levels. Organ examination revealed 

that liver weights were increased in both males and females at the high dose and in the 1000 ppm 

males. At necropsy, all females in the 3000 ppm group had white and enlarged adrenals. In 

addition, adrenal weights were increased in the 1000 and 3000 ppm females. Histopathology 

examinations found an increase of diffuse vacuolation and diffuse hypertrophy of cortical cells in 

the adrenals of all 1000 and 3000 ppm animals.Relative kidney weights were increased in high 

dose males and females. Eight of ten high dose females were observed to have vacuolation of 

interstitial gland cells in their ovaries. 

The LOAEL is 1000 ppm (54.5 mg/kg/day in males, 62.8 mg/kg/day in females) based on the 

hematology and organ weight changes in the liver, organ weight and histopathology effects in the 

adrenals, organ weight increase in the kidneys and histopathological effects observed in the 

ovaries. The NOAEL is 300 ppm (16.5 mg/kg/day in males, 19.0 mg/kg/day in females). 

b) Subchronic Toxicity Study in Mice 

In a subchronic toxicity study (MRID 48542683), cyflumetofen (OK-5101, 97.7% a.i.) was 

administered to 10 SPR ICR mice/sex/dose in diet at dose levels of 0, 300, 1000, 3000 and 10000 

ppm (0, 35.4, 117, 348 and 1200 mg/kg/day in males; 0, 45.0, 150, 447 and 1509 mg/kg/day in 

females) for 90 days. 
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Body weight and food consumption were decreased at ≥ 3000 ppm in females. Organ weight 

examinations revealed increased adrenal weights in high dose males. During necropsy, 9 of 10 

male mice in the 10000 ppm exhibited enlarged adrenals. Histopathological findings showed an 

increased incidence of diffuse hypertrophy of cortical cells in males at the 3000 and 10000 ppm 

doses. Two and seven females exhibited diffuse vacuolation of cortical cells in the adrenals at 

3000 and 10000 ppm, respectively. The degree of severity and incidence of the lesion appeared in 

a dose-related manner, indicating a treatment-related effect. 

The LOAEL is 3000 ppm (348 mg/kg/day in males; 447 mg/kg/day in females), based on 

decreased body weights in females, and diffuse hypertrophy and vacuolation of cortical cells in the 

adrenals in both sexes. The NOAEL is 1000 ppm (117 mg/kg/day in males; 150 mg/kg/day in 

females). 

c) Chronic Toxicity in Rats 

In a chronic toxicity study (MRID 48542696), cyflumetofen (OK-5101, 97.67%) was 

administered to Fischer (F344/DuCrj) rats (50/sex/dose) in the diet at dose levels of 0, 50, 150, 500 

and 1500 ppm (equivalent to 0/0, 1.90/2.31, 5.63/6.92, 18.8/23.3 and 56.8/69.2 mg/kg bw/day in 

males/females, respectively) for one year. Interim sacrifices (10/sex/dose) were performed at 4, 13 

and 26 weeks. All remaining animals were sacrificed at 52 weeks. 

There were no adverse treatment-related effects on mortality, clinical signs, body weight, food 

consumption, haematology, clinical chemistry and urinalysis parameters. Treatment related effects 

were noted in the adrenals of both sexes at the high dose. In females, absolute and relative adrenal 

weights were increased at all scheduled sacrifices, along with diffuse hypertrophy of adrenal 

cortical cells. Effects in males were slightly different with diffuse vacuolation of the cortical cells 

recorded at all interim and terminal sacrifices. An increased incidence of vacuolation of ovarian 

interstitial gland cells was observed in high dose females from week 13 on, along with increased 

ovarian weights at terminal sacrifice. An increased incidence of atrophy of the seminal vesicles 

and coagulating gland were recorded in high dose males at terminal sacrifice only. There were no 

corresponding effects observed during histopathological examination. 

The LOAEL for chronic administration of cyflumetofen in rats is 1500 ppm (equivalent to 

56.8/69.2 mg/kg/day in males/females, respectively) based on diffuse vacuolation of adrenal 

cortical cells and increased incidence of atrophy of the seminal vesicles and coagulating glands in 

males and increased adrenal weights and ovarian weights, diffuse hypertrophy of adrenal cortical 

cells and vacuolation of the ovarian interstitial gland cells in females. The NOAEL is 500 ppm 

(equivalent to 18.8/23.3 mg/kg/day in males/females, respectively). 
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 d) Carcinogenicity in Rats (2004 study) 

In a carcinogenicity study (MRID 48542697), OK-5101(97.67 % a.i.) was administered to 50 

Fischer rats/sex/dose in the diet at dose levels of 0, 150, 500, and 1500 ppm (0, 4.92/6.14, 

16.5/20.3, and 49.5/61.9 mg/kg/day in males/females) for 104 weeks.There were no compound 

related effects on mortality, clinical signs, body weight, food consumption, hematology or gross 

necropsy observations. Diffuse hypertrophy of the adrenal cortex was noted in high dose males 

and females in conjunction with increased adrenal weights. In addition, luminal dilatation of the 

gland of the uterine horn was observed in high dose females. At the doses tested, there was no 

treatment related increase in tumor incidence when compared to controls. The LOAEL is 1500 

ppm (49.5/61.9 mg/kg/day), based on increased adrenal weights, hyperplasia and hypertrophy of 

the adrenal cortex in both sexes, and luminal dilatation of the gland in the uterine horn in females. 

The NOAEL is 500ppm (16.5/20.3 mg/kg/day). There was no treatment related increase in tumor 

incidence when compared to controls. 

e) Carcinogenicity in Rats (2013 study) 

In the 2013 study (MRID 49029701), OK-5101 (cyflumetofen, 97.82 % a.i.) was administered to 

SPF/VAF Fischer rats (F344/DuCrj) (50/sex/dose) in the diet at dose levels of 0 and 6000 ppm (0 

and 250/319 mg/kg/day, ♂/♀) for 52 weeks. Interim sacrifices (10/sex/dose) were performed at 4, 

13, 26 weeks. All remaining animals were sacrificed at 52 weeks. There were no 

treatment-related deaths or effects on food consumption, food efficiency, or in the ophthalmologic 

assessment. In treated females, an increased incidence of soiled fur around the external genital 

area and a consistent decrease in body weight and body weight gain when compared to the control 

group were observed throughout most of the study. Males of the 6000 ppm group had reduced 

body weight gain throughout the study. In treated animals of both sexes, affected hematological 

parameters included decreased platelet count and fibrinogen concentration and elongated 

prothrombin time and activated partial thromboplastin time (APTT). Blood urea nitrogen (BUN) 

was elevated from 26 and 52 week in males and at all sampling points in females and was slightly 

outside of the submitted historical control data range for the females. This observation was 

considered treatment-related in conjunction with increased kidney weights for the treated animals. 

In both sexes at 6000 ppm, absolute and relative liver, kidney and adrenal weights were increased 

at all sacrifice time points. Gross necropsy revealed an increase in the incidence of white colour in 

the adrenal gland in both sexes at 6000 ppm as well as adrenal enlargement in females. 

Treatment-related histological observations included effects noted in the adrenal gland such as 

diffuse hypertrophy of the cortical cell in treated females and diffuse cortical cell vacuolation in 

treated males and focal vacuolation of the cortical cell in treated females with higher incidence of 

these lesions by the end of the study. In treated males, gross lesions in the testis such as atrophy, 

softening, and spots were observed as well as an increased incidence of interstitial cell hyperplasia. 

Atrophy of the acinar cell of the pancreas was also noted in the treated males. In treated females, 

vacuolation of the interstitial gland cell of the ovary was observed. 

The LOAEL was 6000 ppm (250/319 mg/kg/day, ♂/♀) based on increased adrenal weights 

accompanied by gross pathology and histopathology lesions noted in both sexes, vacuolation of 

the interstitial gland cell of the ovary and hyperplasia of the interstitial cell of the testes. A NOAEL 

was not set in this study. 
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f) Carcinogenicity Study in Mice (2004 study) 

In a carcinogenicity study, OK-5101(97.67 % a.i.) was administered to 52 CD-1 mice/sex/dose in 

the diet at dose levels of 0, 150, 500, 1500 and 5000 ppm (0, 15.5/14.3, 54.3/48.1, 156/144, and 

537/483 mg/kg/day in males/females) for 78 weeks. 

There were no compound-related effects on mortality, clinical signs, body weight, food 

consumption, hematology or gross necropsy observations at any dose level. Diffuse adrenal 

cortical cell vacuolation was noted in 5000 ppm males and females, with a corresponding increase 

in adrenal weight in males. At the doses tested, there was no treatment related increase in tumor 

incidence when compared to controls. 

The LOAEL is 5000 ppm (537/483 mg/kg/day), based on an increased incidence of diffuse adrenal 

cortical cell vacuolation in males and females, and an increase in adrenal weight in males. The 

NOAEL is 1500 ppm (156/144 mg/kg/day). There was no treatment related increase in tumor 

incidence when compared to controls. 

 g) Carcinogenicity Study in Mice (2013 study) 

In the 2013 carcinogenicity study, BAS 9210 I (cyflumetofen, 97.82 % a.i.) was administered to 

SPF ICR (Crj:CD1) mice (52/sex/dose) in the diet at dose levels of 0 and 10,000 ppm (0 and 

1143/1132 mg/kg/day in males/females) for 78 weeks. 

There were no compound-related effects on mortality, body weight, food consumption, or 

hematology parameters at the dose tested. Diffuse adrenal cortical cell vacuolation and deposition 

of brown pigment in the cortico-medullary junction of the adrenals was observed in treated 

animals of both sexes. Treated females exhibited a significant increase in the incidence of 

pale-colored skin and pale-colored eye/eyelid, increased adrenal weights, enlarged spleen and an 

increased incidence of extramedullary hematopoiesis in the spleen. 

The LOAEL for this confirmatory study is 10,000 ppm (1143/1132 mg/kg/day), based on clinical 

signs of toxicity, increased adrenal weights, enlarged spleen and an increased incidence of 

extramedullary hematopoiesis in the spleen of treated females and an increased incidence of 

diffuse adrenal cortical cell vacuolation and deposition of brown pigment in the cortico-medullary 

junction of the adrenals in both sexes. A NOAEL was not identified for this study. 

At the dose tested, there was no treatment-related increase in tumor incidence when compared to 

controls. Dosing was considered adequate as animals were dosed above the limit dose of 1000 

mg/kg/day. 
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5. Mode of Action Studies 

There is no mode of action (MOA) data available for thyroid c-cell adenoma/adenocarcinoma at 

this time. However, MOA data were submitted for the Leydig cell tumors (LCT). The CARC did 

not review the MOA for the LCTs since the MOA for development of this lesion depends on 

transient, rat-specific, hormonally mediated mechanisms that have low relevance to humans due to 

the qualitative and quantitative differences between rat and human Leydig cells(Boorman et al.

1990). 

V. COMMITTEE’S ASSESSMENT OF THE WEIGHT-OF-THE-EVIDENCE 

1. Carcinogenicity

 The carcinogenic potential of cyflumetofen was evaluated following dietary administration 

to male and female Fischer 344 rats. Two studies were conducted in the rats. One study was 

conducted at doses of 0, 150, 500 and 1500 ppm while a second high dose study was conducted at 

0 and 6000 ppm. There was no evidence of carcinogenicity in female rat at any dose level. There 

was limited evidence of carcinogenicity characterized by the presence of thyroid c-cell tumors and 

interstitial cell tumors of the tested in male rats only at the highest dose tested (HDT). The doses 

tested were determined to be adequate to assess the carcinogenic potential of cyflumetofen in male 

and female rats. 

The thyroid c-cell tumors were determined to be treatment-related based on the following 

considerations: a statistically significant trend, and a pair-wise significance (both at p < 0.05) for 

thyroid c-cell adenocarcinomas when compared to controls; a statistically significant trend (p < 

0.05) and a pair-wise significance (p<0.01) for thyroid c-cell adenomas and/or adenocarcinomas 

combined; and the incidences of the adenocarcinomas (31%) and the combined tumors (57%) 

exceeded the historical control range of the testing laboratory (c-cell adenocarcinoma, 6-18%, and 

combined c-cell adenoma/carcinomas, 26-50%). 

The testicular interstitial cell tumors, although exacerbated by treatment were not considered to be 

biologically relevant since this tumor (Leydig cell, LCT) are extremely common in the F344 rat, 

with a reported background incidence of 56-100% in 2-year cancer studies. The reasons for the 

different background incidence rate for LCT among species stem from both quantitative and 

qualitative differences in the Leydig cell response to hormonal stimuli. The rat Leydig cell is 

extremely sensitive to slight changes in circulating luteinizing hormone (LH) levels. Among rat 

strains, the F344 rat is particularly susceptible to this process and is not considered a relevant 

model for studying LCT. Because of the differences present between the human and the rat Leydig 

cells, non-genotoxic compounds that cause LCT in rats have little relevance to humans. By 

contrast, the incidence rate in humans of LCT is very low (i.e., 0.00004%). Similarly, rats are 

known to have approximately 13-times more LH receptors per cell than humans (Hutaniemi, 

1983). 
PC Code: 138831 FINAL

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The data with Cyflumetofen supports this species and strain-specific effect on the Leydig Cells. 

Other than at a high dose with the F344 rat, there was no treatment related effects observed on the 

Leydig cell in other tested rat strains (Wistar) and species (dog, mouse), no matter the dose level or 

the duration of dosing. 

The carcinogenic potential of cyflumetofen was evaluated following dietary administration to 

male and female CD-1 mice. Two studies were conducted in the mice. One study was conducted at 

doses of 0, 150, 500 and 5000 ppm while a second high dose study was conducted at 0 and 10,000 

ppm. There was no evidence of carcinogenicity in male or female mice at any dose level. The 

doses tested were determined to be adequate to assess the carcinogenic potential of cyflumetofen 

in male and female mice. 

2. Mutagenicity 

The mutagenic potential of cyflumetofen, its metabolites, and an impurity was tested in in vitro

and in vivo studies. There was no concern for mutagenicity for the parent, the metabolites or the 

impurity. Consequently, mutagenicity can be ruled out as a possible mode of action for tumor 

formation. 

3. Structure Activity Relationship 

No structure-activity relationship information is available in the OncoLogic expert system. 

4. Mode of Action 

No studies were submitted to evaluate the MOA for thyroid tumors. However, MOA data were 

submitted for the Leydig cell tumors (LCT). The MOA for the Leydig cell tumors was not 

reviewed since this tumor type has a high background rate in the Fischer 344 rats and is of low 

relevance for humans 

VI. CLASSIFICATION OF CARCINOGENIC POTENTIAL

In accordance with the EPA's Final Guidelines for Carcinogen Risk Assessment (March, 2005), 

the Cancer Assessment Review Committee (CARC) classified cyflumetofen as “Suggestive 

Evidence of Carcinogenic Potential”. This classification is based on the presence of a single tumor 

type (thyroid c-cell) in one sex (male) and one species (rat), and the lack of concern for 

mutagenicity. 

VII. QUANTIFICATION OF CARCINOGENIC POTENTIAL

When there is suggestive evidence of carcinogenicity, the Agency does not attempt a 

dose-response assessment as the nature of the data generally would not support one. Therefore, the 

Agency has determined that quantification of risk using a non-linear approach (i.e. the chronic 

reference dose) will adequately protect for all chronic toxicity, including carcinogenicity, likely to 

result from exposure to cyflumetofen.
PC Code: 138831 FINAL

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VIII. BIBLIOGRAPHY

MRID CITATION

48542682 Repeated Dose 90-day Oral Toxicity Study in Rats. The Institute of Environmental 

Toxicology. Laboratory report number: IET 01-0061. Study report date: 

17-June-2004. Applicant Report Number: OTSA-0014 (EN)-FR. DACO 4.3.1 

48542683 Repeated Dose 90-day Toxicity Study in Mice. The Institute of environmental 

Toxicology. Laboratory report number: IET 01-0111. Study report date: 

21-June-2004. Applicant Report Number: OTSA-0042 (EN)-FR.DACO 4.3.1. 

48542696 Repeated Dose 1-year Oral Toxicity Study in Rats. The Institute of 

Environmental Toxicology, Ibaraki, Japan. Laboratory report number IET 

01-0124. June 22, 2004. DACO 4.4.1 

48542697 Carcinogenicity Study in Rats. The Institute of Environmental Toxicology, 

Ibaraki, Japan. Laboratory report number: IET 01-0125. Study report date: 

29-July-2004. Applicant Report Number: OSTA-0046(EN)-FR. DACO 4.4.2. 

48542698 Carcinogenicity Study in Mice. The Institute of Environmental Toxicology, 

Ibaraki, Japan. Laboratory report number: IET 02-0039. Study report date: 

27-July-2004. Applicant Report Number: OTSA-0061 (EN)-FR. DACO 4.4.3. 

49226601 BAS 9210 I (Cyflumetofen): Carcinogenicity Study in Rats. The Institute of 

Environmental Toxicology, Ibaraki, Japan, October 7, 2013. IET 11-0002 

49209101 BAS 9210 I (Cyflumetofen): Carcinogenicity Study in Mice. The Institute of 

Environmental Toxicology, Ibaraki, Japan. Laboratory report number: IET 

11-0016. Study report date: 08-August-2013. Applicant Report Number: 

2013/1251154. DACO 4.4.3. 

48542687 Bacterial Reverse Mutation Test. The Institute of Environmental Toxicology, 

Ibaraki, Japan. Laboratory report number: IET 01-0033. Study report date: 

06-August-2001. Applicant Report Number: OTSA-0009(EN)FR. DACO 4.5.4. 

48542691 BAS 9210 I (Cyflumetofen) – In Vitro Chromosome Aberration Assay in V79 

Cells. Experimental Toxicology and Ecology, BASF SE, Germany. Laboratory 

report number: 32M0510/094436. Study report date: 25-January-2011. 

Applicant Report Number: 2010/1151897. DACO 4.5.6. 

48542689 OK-5101: In Vitro Mammalian Chromosome Aberration Test. The Institute of 

Environmental Toxicology, Ibaraki, Japan. Laboratory report number: IET 

01-0034. Study report date: 15-December-2003. Applicant Report Number: 

OTSA-0011 (EN)-FR. DACO 4.5.6. 

48542692 Evaluation of the Mutagenic Activity of OK-5101 in an In Vitro Mammalian Cell 

Gene Mutation Test with L5178Y Mouse Lymphoma Cells. Noton B.V., The 

Netherlands. Laboratory report number: 485622. Study report date: 

06-November-2007. Applicant Report Number: OTSA-0362-FR. DACO 4.5.5. 

48542694 OK-5101: Micronucleus Test in Mice. The Institute of Environmental 

Toxicology. Laboratory report number: IET 01-0035. Study report date: 

16-December-2003. Report Number: OTSA-0019(EN)-FR. DACO 4.5.7. 

48542695 Evaluation of DNA Repair Inducing Ability of OK-5101 in Male rat Hepatocytes 

(In Vivo Rat Hepatocyte DNA-Repair Assay). Notox B.V., Hertogenbosch, The 
PC Code: 138831 FINAL

27 

Netherlands. Laboratory report number: 486284. Study report date: 

30-October-2007. Applicant Report Number: 2007/1067386. DACO 4.5.8. 

48542710 Evaluation of the Mutagenic Activity of B-1 in the Salmonella typhimurium

Reverse Mutation Assay and the Escherichia coli Reverse Mutation Assay (With 

Independent Repeat). Notox B.V., Hertogenbosch, The Netherlands. Laboratory 

report number: 396113. Study report date: 15-June-2004. Applicant Report 

Number: OTSA-0171. DACO 4.5.4. 

48542712 Evaluation of the Mutagenic Ability of B-1 in an In Vitro Mammalian Cell Gene 

Mutation Test with L5178Y Mouse Lymphoma Cells (With Independent Repeat). 

Notox B.V., Hertogenbosch, The Netherlands. Laboratory report number: 

396179. Study report date: 22-December-2004. Applicant Report Number: 

OTSA-0172. DACO 4.5.5. 

48542711 Evaluation of the Ability of B-1 to Induce Chromosome Aberrations in Cultured 

Peripheral Human Lymphocytes. Notox B.V., Hertogenbosch, The Netherlands. 

Laboratory report number: 396146. Study report date: 21-June-2004. 

Applicant Report Number: OTSA-0173. DACO 4.5.6. 

48542713 Evaluation of DNA Repair Inducing Ability of B-1 in Male Rat Hepatocytes (In 

Vivo Rat Hepatocyte DNA-Repair Assay). Notox B.V., Hertogenbosch, The 

Netherlands. Laboratory name. Laboratory report number: 490348. Study report 

date: 23-April-2009. Applicant Report Number: 2009/1126680. DACO 4.5.8. 

48542715 Evaluation of the Mutagenic Activity of 2-(Trifluoromethyl) benzamide, B-3 in 

the Salmonella typhimurium Reverse Mutation Assay and the Escherichia coli

Reverse Mutation Assay (With Independent Repeat). Notox B.V., 

Hertogenbosch, The Netherlands. Laboratory report number: 489612. Study 

report date: 23-April-2009. Applicant Report Number: 2009/1126681. DACO 

4.5.4. 

48542716 Evaluation of the Ability of 2-(Trifluoromethyl)benzamide, B-3 to Induce 

Chromosome Aberrations in Cultured Peripheral Human Lymphocytes (with 

Repeat Experiment). Notox B.V., Hertogenbosch, The Netherlands. Laboratory 

report number: 489613. Study report date: 16-April-2009. Applicant Report 

Number: 2009/1126682. DACO 4.5.6. 

48542717 Evaluation of the Mutagenic Ability of 2-(Trifluoromethyl)benzamide, B-3 in an 

In Vitro Mammalian Cell Gene Mutation Test with L5178Y Mouse Lymphoma 

Cells (With Independent Repeat). Notox B.V., Hertogenbosch, The 

Netherlands. Laboratory report number: 489614. Study report date: 

20-April-2009. Applicant Report Number: 2009/1126683. DACO 4.5.5. 

48542718 Evaluation of DNA Repair Inducing Ability of 2-(trifluoromethyl)benzamide, B-3 

in Male Rat Hepatocytes (In Vivo Rat Hepatocyte DNA-Repair Assay). Notox 

B.V., Hertogenbosch, The Netherlands. Laboratory report number: 490347. 

Study report date: 23-April-2009. Applicant Report Number: 2009-1126684. 

DACO 4.5.8. 

48542670 Assessment of Acute Oral Toxicity with AB-13 (Analytical Grade) in the Rat 

(Acute Toxic Class Method). Notox B.V., Hertogenbosch, The Netherlands. 

Laboratory report number: 407835. Study report date: 09-August-2004. 

Applicant Report Number: OTSA-0197. DACO 4.2.1. 
PC Code: 138831 FINAL

28 

48542688 Evaluation of the Mutagenic Activity of AB-13 (Impurity of OK-5101) in the 

Salmonella typhimurium Reverse Mutation Assay and the Escherichia coli

Reverse Mutation Assay (With Independent Repeat). Notox B.V., 

Hertogenbosch, The Netherlands. Laboratory report number: 407846. Study 

report date: 19-August-2004. Applicant Report Number: 2004/1038340. DACO 

4.5.4. 

48849413 Evaluation of the Mutagenic Activity of AB13 (Impurity of OK-5101) in an In 

Vitro Mammalian Cell Gene Mutation Test with L5178Y Mouse Lymphoma 

Cells (With Independent Repeat). Notox B.V., Hertogenbosch, The 

Netherlands. Laboratory report number: 408408. Study report date: 

14-July-2004. DACO 4.5.5. 

48542690 Evaluation of the Ability of AB-13 (Impurity of OK-5101) to Induce 

Chromosome Aberrations in Cultured Peripheral Human Lymphocytes (With 

Repeat Experiment). Notox B.V., Hertogenbosch, The Netherlands. Laboratory 

report number: 407857. Study report date: 13-July-2004. Applicant Report 

Number: OTSA-0193. DACO 4.5.6. 

49029701 BAS 9210 I (Cyflumetofen): Repeated dose 1-year oral toxicity study in rats. 

Institute of Environmental Toxicology, Japan. Laboratory report number IET 

11-0001; 70C0510/09X067. Study report date: 21-Nov-2012. Applicant Report 

Number 2012/1343340. 

49209101 BAS 9210 I (Cyflumetofen): Carcinogenicity Study in Mice. The Institute of 

Environmental Toxicology, Ibaraki, Japan. Laboratory report number: IET 

11-0016. Study report date: 08-August-2013. Applicant Report Number: 

2013/1251154. 

49226601 BAS 9210 I (Cyflumetofen): Carcinogenicity Study in Rats. The Institute of 

Environmental Toxicology, Ibaraki, Japan. Laboratory report number: IET 

11-0002. Study report date: 07 October, 2013. Applicant Report Number: 

2013/1345430.

49250601 Mode of Action for Leydig Cell Tumors in a High Dose 2-yr Rat Cancer 

Study with Cyflumetofen. BASF Corporation, 26 Davis Drive, Research Triangle 

Park, NC 27709. Study report date: October 23, 2013. BASF Registration 

Document Number 2013/7002798. 

US EPA Lori L. Brunsman (2013). Cyflumetofen Qualitative Risk Assessment Based On 

F344 Rat Dietary Study. TXR No.: 0056837 

Boorman 

et al., 1990 

Boorman GA, Chapin RE, and Mitsumori K (1990).Testis and epididymis. In: 

Pathology of the Fischer 

Rat—Reference and Atlas, GA Boorman, SL Eustis, MR Elwell, CA Montgomery, 

and WF 

MacKenzie (eds). Academic Press, New York, San Diego, pp. 405–418.