Bosutinib As Therapy For Chronic Phase Chronic Myeloid Leukemia Following Failure With Imatinib Plus Dasatinib and/Or Nilotinib: 36-Month Update
Authors: Cortes Jorge E. , Khoury H. Jean , Kantarjian Hagop M. , Lipton Jeff H. , Kim Dong-Wook , Conlan Maureen G. , Leip Eric , Turnbull Kathleen , Brümmendorf Tim H. , Gambacorti-Passerini Carlo 
Published: November 2019

Abstract
Bosutinib (BOS) is an oral dual Src/Abl tyrosine kinase inhibitor (TKI). This open-label, phase 1/2 study evaluated BOS in patients (pts) with chronic phase chronic myeloid leukemia (CP CML) following TKI failure.
Pts (n=118) aged ≥18 y with prior imatinib (IM) failure plus dasatinib (D) resistance (D-R; n=38) or intolerance (D-I; n=50), nilotinib (N) resistance (N-R; n=26), or N-I or D-R/I + N-R/I (n=4) received BOS starting at 500 mg/d. Median (range) age was 56 (20–79) y; time from CML diagnosis was 6.6 (0.6–18.3) y; follow-up duration was 33.1 (0.3–84.8) mo; BOS treatment duration was 8.5 (0.2–78.1) mo. Escalation to BOS 600 mg/d occurred in 21 (18%) pts. For the last enrolled pt, time from first dose was ≥36 mo; 19% are still receiving BOS.
Confirmed complete hematologic response (CHR) was newly attained or maintained from baseline by 73% of pts (Table). Major cytogenetic response (MCyR) was attained/maintained by 40% of pts (32% with complete cytogenetic response [CCyR]). Kaplan-Meier probability of maintaining CHR or MCyR at 3 y was 65%.IM + D-R (n=38)IM + D-I (n=50)IM + N-R (n=26)IM + N-I or D-R/I + N-R/Ia (n=4)Total (n=118)Evaluable,b n3849254116Confirmed CHR, n (%)26 (68)37 (76)19 (76)3 (75)85 (73)Probability of maintaining CHR at 3 yc57%74%62%NR65%Evaluable,b n3645254110MCyR, n (%)14 (39)19 (42)9 (36)2 (50)44 (40)CCyR , n (%)8 (22)18 (40)7 (28)2 (50)35 (32)Probability of maintaining MCyR at 3 yc29%87%75%NR65%Treated, n3850264118PD/death at 3 yd26%16%35%NR25%OS at 2 yc80%83%92%NR84%D=dasatinib; I=intolerant; IM=imatinib; N=nilotinib; NR=not reported (small sample size); OS=overall survival; PD=progressive disease; R=resistant.aIncludes 3 pts with prior exposure to all 3 TKIs and 1 N-I pt.bReceived ≥1 BOS dose and had a valid baseline efficacy assessment for the respective endpoint.cBased on KM estimates.dBased on cumulative incidence adjusting for competing risk of treatment discontinuation without PD or death.
Of 85 pts with known baseline mutation status, 19 unique BCR-ABL mutations occurred in 39 (46%) pts, including 7 (8%) with T315I. Responses were seen across mutations, but were low in pts with T315I (29% CHR; 14% MCyR). In pts with ≥1 mutation, excluding T315I, 75% had CHR and 40% had MCyR.
38 pts had known baseline and end of treatment mutation status; 8/38 had ≥1 new mutation (V299L, n=4; T315I, n=2; F359C, G250E, L248V, n=1 each); 7/8 discontinued BOS due to disease progression or lack of efficacy.
Cumulative incidence of on-treatment transformation to accelerated-phase (AP) CML at 3 y was 4%; 77% discontinued without transformation. No pt transformed to blast-phase (BP); no transformations occurred after 2 y. Cumulative incidence of on-treatment progression (transformation to AP/BP CML, increasing white blood cell count [doubling over ≥1 mo with 2nd count >20×109/L and confirmed ≥1 wk later], or loss of confirmed CHR or unconfirmed MCyR) or death at 3 y was 25%; 55% of pts discontinued without an event. Overall survival (OS) at 2 y was 84% (Table; 3-y OS estimates unreliable; pts followed for OS for only 2 y after BOS discontinuation]).
Overall, 96 (81%) pts discontinued treatment, the most common primary reasons were adverse event (AE; n=29 [25%]), disease progression (n=25 [21%]), or unsatisfactory efficacy (n=23 [19%]). 26 (22%) deaths occurred on study, 5 within 30 d of last BOS dose. Most deaths were due to disease progression (n=11 [9%]) or AE (n=11 [9%], including 1 death reported as treatment-related due to lower gastrointestinal bleeding). 4 deaths had unknown cause 33–615 d after the last BOS dose.
Non-hematologic treatment-emergent AEs in ≥20% of pts (all grades; grade 3/4) were diarrhea (83%; 9%), nausea (48%; 1%), vomiting (38%; 1%), rash (27%; 3%), headache (26%; 3%), fatigue (23%; 2%), and abdominal pain (24%; 1%); common hematologic toxicities included thrombocytopenia (38%; 26%), neutropenia (20%; 15%), and anemia (19%; 7%). Cardiac events occurred in 15% of pts (8% grade 3/4). Grade 3/4 laboratory abnormalities in ≥10% of pts were thrombocytopenia (26%), neutropenia (20%), lymphopenia (16%), and hypermagnesemia (12%). 78 (66%) pts had ≥1 dose delay; 59 (50%) had ≥1 dose reduction. 31 (26%) pts discontinued BOS due to AE, most commonly thrombocytopenia (7%).
BOS continues to demonstrate durable efficacy and manageable toxicity after ≥36 mo follow-up in CP-CML pts following resistance or intolerance to multiple TKIs.

Disclosures:
Cortes: Pfizer: Consultancy, Research Funding; Novartis: Research Funding; Bristol Myer Squibb: Research Funding; Teva: Consultancy, Research Funding; Ariad: Consultancy, Research Funding. Kantarjian:Pfizer Inc: Research Funding. Lipton:Novartis: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bristol Myers Squib: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Ariad: Equity Ownership, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau. Kim:Pfizer: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; BMS: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding. Conlan:Pfizer Inc: Employment. Leip:Pfizer Inc: Employment. Turnbull:Pfizer Inc: Employment. Brümmendorf:Ariad: Consultancy; Patent on the use of imatinib and hypusination inhibitors: Patents & Royalties; Pfizer: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria. Gambacorti-Passerini:Bristol Myer Squibb: Consultancy; Pfizer Inc: Consultancy, Research Funding; Novartis: Consultancy.