# Presentation: 209531

## Studying the Risk of Cancer with Topical Calcineurin Inhibitor Use in Children: Design Issues

**Lois La Grenade, MD, MPH**
***Center for Drug Evaluation & Research***
***Office of Drug Safety***

## Outline

**Observational studies - general methods**
**Methods for risk of cancer with long term use of calcineurin inhibitors (CI) in children with atopic dermatitis (AD)**

## Epidemiologic Methods

**Observational Studies**
**Case Control**
**Cohort**
**Registries**

## Case Control Studies

**Retrospective**
**Start with disease of interest (cases), **
**Compare with people without disease (controls)**
**Compare frequency of the exposure of interest between cases & controls**

## Case Control Studies - Advantages

**Less expensive**
**Relatively quick**
**Generally useful for studying most rare events, with common exposures**

## Case Control Studies - Disadvantages

**Subject to several biases **
**Recall**
**Selection**
**Unsuitable for studying diseases with very long latency periods, e.g. cancer**
**Difficult for rare exposures**

## Cohort Studies

**Compare exposed vs. non-exposed persons**
**Start with a defined group of people (defined by exposure, disease, place of residence etc.)**
**Followed through time for occurrence of disease(s) of interest**
**Prospective **

## Cohort Studies - Advantages

**Cases & exposure determined prospectively, so recall bias minimized**
**All cases can potentially be captured, so selection bias reduced**
**Can study several outcomes or diseases **
**Most closely resemble experimental design – toxin administered, then follow for outcome**
**Consequent high acceptance by scientific community**

## Cohort Studies - Disadvantages

**More expensive**
**Large sample sizes for rare diseases**
**Long**
**Problems from losses to follow-up**

## Retrospective Cohort Studies

**Can be used to overcome disadvantages of prospective cohorts viz. length**
**Use a preexisting cohort, e.g. occupational cohort, cohort exposed to a drug of interest**
**Instead of comparison controls, can compare disease with population incidence rates (Standardized Incidence Ratio - SIR)**

## Registries

**Exposure based – occupational, drug exposures**
**Disease based – State & National Cancer Registries**
**Complete (usually mandatory) – all subjects with exposure/disease captured**
**Incomplete (usually voluntary) – only some cases/exposed  persons captured**

## Uses of Registries in Epidemiology

**Exposure registries – cases ascertained in exposure cohort e.g. cohort of drug exposed people **
**Case based registries – as source of cases for case control study**
**Complete registries generally far more useful**
**Can be used to determine incidence rates when based in defined population**
**Incidence of rare events with rare exposures**

## Topical Calcineurins & atopic dermatitis in children

## Cancer Risk with Calcineurin Inhibitor (CI) Use in Children with AD 

**Special problems with cancer studies**
**Rare events, particularly in the young**
**Very long latency, i.e. many years between exposure & clinically apparent cancer **
**Prospective method (cohort or registry) ideal**

## Cohort Design

**Prospective **
**Exposure assessment, accurate, standardized**
**Dose, duration of topical CI can be assessed**
**Case ascertainment, complete, accurate**
**Data on confounding/risk factors**

## Cohort Study - Indication

**There is good evidence of an association between a disease & an exposure**
**Clinical studies**
**Case control studies**
**Other studies e.g. animal studies***
**Introduction of a new agent that requires monitoring for its possible association with several diseases****

- *Gordis, Epidemiology, 1996
- **Kelsey et al, Methods in Observational Epidemiology,1996

## “International Monitoring of Adverse Drug Reactions of Long Latency”

**Fletcher AP, Griffin JP**
***Adverse Drug React. Toxicol. Rev. 1991, 10 (4) 209 – 230***
***   “******for adverse reactions of long latency to be detected methods have to be used that permit observation of the patient to be followed for many months or years.....An essential requirement is the identification of a cohort of patients exposed to a particular drug ....who may be accessed at specified intervals of time.”***

## Cohort Study Design - Cancer Risk with Calcineurin Inhibitor (CI) Use in Children with AD 

**Background**
**Objectives**
**Population**
**Sample Size/Power**
**Exposure definition & assessment**
**Endpoint (cancers) definition & ascertainment**
**Measures to reduce bias – losses to follow-up**
**Analysis Plan**

## Background

**Enhanced photocarcinogenicity with both topical CI vehicles **
**Carcinogenicity studies – signal for lymphoma & other systemic malignancies**
**Oral CI use associated with ****↑ risk of lymphoma, cutaneous & other malignancies**

## Objective

**To investigate the risk of developing cutaneous & systemic malignancies in children with atopic dermatitis (AD) who have long term intermittent treatment with topical CIs**

## Outcomes of Interest

**Cutaneous malignancies**
**Melanoma**
**Non-melanoma (basal & squamous)**
**Systemic**
**Lymphoma (Hodgkin’s, NHL)**
**Others**
** ****Additional cutaneous end points, e.g. actinic keratoses?**

## Population

**Traditional study**
**Cohort of children (aged 2 - 16 years) with AD**
**Follow  for 10 – 15 years**
**Document treatment type, response, confounding factors e.g. sunlight exposure, skin type, disease severity **
**Document occurrence of malignancies as they occur**
**At end of follow up, compare incidence in CI treated vs. non-CI treated group**

## Cohort - Population

**Traditional study - difficulties**
**Very long**
**Very large sample size**
**May find that most patients have used both CI and non-CI treatment regimens (or vice versa) and comparison may be difficult**

## Cohort – Population (Alternate method)

**Cohort of CI users (aged 2 – 16 years) with AD**
**Follow subjects for minimum 10 year period**
**Use age specific population incidence rates for cancer as comparator **
**(Standardized Incidence Ratio, SIR)**
**Similar to occupational epidemiology methods**

## SIR Approach - Difficulties

**No US national incidence rates for most cutaneous malignancies**
**May have to extrapolate from data from other countries, e.g. Finland, or from US local data e.g. Southeastern Arizona**

## *US Age Specific Incidence of all Malignancies per 100,000, by gender

***US Age Specific Incidence of all Malignancies per 100,000, by gender**

- *Surveillance, Epidemiology, and End Results (SEER) Program (www.seer.cancer.gov) SEER*Stat Database: Incidence - SEER 9 Regs Public-Use, Nov 2002 Sub (1973-2000), National Cancer Institute, DCCPS, Surveillance Research Program, Cancer Statistics Branch, released April 2003, based on the November 2002 submission.

## Age Specific Incidence of SCC per 100,000, by gender, Southeastern Arizona*

**Age Specific Incidence of SCC per 100,000, by gender, Southeastern Arizona***

- *Harris RB et al, 2001, JAAD (43):4, 528-536

- Males

- Females

## Age Specific Incidence of BCC per 100,000, by gender, Southeastern Arizona*

**Age Specific Incidence of BCC per 100,000, by gender, Southeastern Arizona***

- *Harris RB et al, 2001, JAAD (43):4, 528-536

- Males

- Females

## Power/Sample Size Calculations*

| Background Rate/10,000 pop | RR | # in each group | Total |
| --- | --- | --- | --- |
| 6 | 3 | 10,300 | 20,600 |
| 6 | 4 | 6000 | 12000 |
| 6 | 5 | 4000 | 8000 |

- *Background rate 6/10,000 represents annual incidence rate for all cancers in 25 - 29 age group, SEER Cancer Statistics Review 1973-1999
- Power 80%,  0.05

## Power & Sample Size Calculations

| Background Rate* | RR
 | # in Group |
| --- | --- | --- |
| 2/10,000 | 2 | 62,000 |
|  | 4 | 14,000 |
|  | 6 | 8,000 |
|  | 8 | 6,000 |

- *Annual incidence rate for all cancers in 15 - 19 age group, SEER Cancer Statistics Review 1975-2000
- Power 80%,  0.05

## Power & Sample Size Calculations

| Background Rate* 24.1/million | RR
 | # in Group |
| --- | --- | --- |
|  | 2 | 514,000 |
|  | 4 | 115,000 |
|  | 6 | 62,000 |
|  | 8 | 42,000 |
|  | 10 | 32,000 |

- *Annual incidence rate for lymphoma in 0 - 19 age group, SEER Cancer Statistics Review 1973-1999
- Power 80%,  0.05

## Probability of finding no event with defined sample sizes – Lymphoma*

| N = 10,000 |  | N = 20,000 |  |
| --- | --- | --- | --- |
| RR | Probability (%) | RR | Probability (%) |
| 2 | 61 | 2 | 38 |
| 4 | 38 | 4 | 15 |
| 6 | 24 | 6 | 6 |
| 8 | 15 | 8 | 2 |
| 10 | 9 | 10 | 1 |

- *Incidence 24.1/million, Age 0-19 years, SEER Cancer Statistics Review 1973-1999

## Probability of finding no event with defined sample sizes

- N=10,000

- N=20,000

***Lymphoma incidence 24.1/million, Age 0-19 years**

## Sample Size/Power

**Multicenter, multinational cohort would boost sample size and power considerably**
**Use of additional end points, e.g. AK, might also increase power**

## AK as additional End Point

**Actinic Keratoses (AK) **
** ****precancerous skin lesions, proliferation of abnormal keratinocytes within epidermis**
**SCC in situ**
**may become SCC (60% of all SCC may start as AK*)**
**Very rare in young people**

- * Fu W & Cockerell C, 2003 Arch Dermatol,139:66-70

## Exposure Definition

**Need to define “long term intermittent exposure” to CIs**
**At enrollment**
**Suggestions**
**6 weeks/3 months continuous or intermittent use**
**30 GM over 6 weeks**

## Exposure Assessment (Enrollment & During Study)

**Possibilities**
**Prescription + Self report by care giver**
**Return unused portions of tubes**
**Weigh unused tubes/portions**
**Consider additional burden on participants (losses to follow-up) vs. more accurate information**

## Ascertainment of Malignancies

**Pathologic/histologic definitions**
**ICD codes**
**Systemic malignancies could be ascertained by linkage with state/national cancer registries, once a unique identifier was obtained for each subject at baseline**
**But not true for most cutaneous malignancies**
**Self reporting of cutaneous malignancies unreliable**

## Ascertainment of Cutaneous Malignancies

**Most state & national cancer registries collect limited data on skin malignancies (usually data on invasive melanomas only)**
**Non-melanoma skin cancers (basal & squamous cell cancers) often treated in office procedure**
**Basal cell cancers (BCC) & AK may be treated with cryotherapy or electrocautery, without even histology**

## Ascertainment of Cutaneous Malignancies

**Best done by periodic (annual?) physical examination (PE) of the skin by physician, preferably a dermatologist**
**PE particularly important for good capture of all cutaneous outcomes & hence early, accurate assessment of the risk**

## Follow-up

**Duration**
**Minimum 10 years for each subject, in keeping with long latent period for cancers**

## Minimizing Losses to Follow-up

**Losses to follow-up **
**Important source of bias in cohort studies of long duration**
**So vigorous methods will have to be used to reduce losses to follow-up **
**Statistical methods to handle losses to follow-up**

## Statistical Analysis Plan

**Crude & adjusted incidence rate, **
**SIR**
**Methods for handling losses to follow-up**

## Registry - Cancer Risk with Calcineurin Inhibitor (CI) Use in Children with AD 

**Ideal:**
**Exposure registry**
**Registration of **_**all **_**users of CIs (probably mandatory), prospective collection of unique identifier (e.g. SSN)**
**Link to state/national cancer registries for detecting systemic malignancies **
**Would still need periodic examination by physician to ascertain skin cancers**

## Mandatory Registry - Advantages

**All users registered**
**Minimal survivor bias, minimal losses to follow-up**
**If ascertainment of malignancies were also complete, registry would provide fastest incidence results**

## Mandatory Registry - Disadvantages

**Poor acceptance by physicians & patients **
**Expensive**
**No accurate exposure assessment**
**No data on confounding factors**
**Not possible to ascertain most skin cancers**

## Summary

|  | Cohort | Registry (mandatory) | Case Control |
| --- | --- | --- | --- |
| Exposure Assess. | Good | Fair | Poor |
| Outcome Assess. | Good | Incomplete | Incomplete |
| Duration | Long | Long | Shorter |
| Expense | +++ | ++ | + |
| Sample size | Large | Large | Smaller |
| Risk factors | Yes | Incomplete | Poor |
| Incidence | Yes | Incomplete  | No |
| RR | Yes | No | No (OR) |
| SIR | Yes | Not for skin cancers | No |

## Practical Issues 

**Duration of follow-up**
**Sample Size/Power**
**Endpoint (cancers) ascertainment**
**How often, by whom**
**Measures to reduce bias **
**losses to follow-up**
**What level of uncertainty?**

## Acknowledgements

**Yi Tsong, PhD. Actg. Deputy Director, QMR, OB**
**David Graham, MD, MPH, Associate Director for Science, ODS**