Efficacy and Tolerability of Bosutinib and Imatinib in Older Versus Younger Patients with Newly Diagnosed Chronic Phase Chronic Myeloid Leukemia–BELA Trial

Abstract 4442

Bosutinib (BOS) is an orally active, dual Src/Abl kinase inhibitor with activity and manageable toxicity in the phase 3 BELA trial of patients (pts) with newly diagnosed (≤6 mo) chronic phase (CP) chronic myeloid leukemia (CML).

The current analysis of the BELA trial summarizes the activity and tolerability of BOS 500 mg/d and imatinib (IM) 400 mg/d among older (≥65 y; BOS n = 30; IM n = 27) versus younger pts (<65 y; BOS n = 220; IM n = 225). Sokal risk scores were balanced between treatment arms but, as expected, higher among older pts (4% low; 72% intermediate; 25% high) versus younger pts (39% low; 44% intermediate; 17% high). Minimum follow-up duration was 24 mo. BOS was discontinued by 37% of pts (57% older vs 35% younger; P = 0.023); difference between age groups was primarily due to adverse events (AEs; 39% vs 22%; most commonly increased alanine aminotransferase [ALT]). IM was discontinued by 27% of pts (35% older vs 28% younger; P= 0.496); disease progression was the primary reason.

In the intent-to-treat population, cumulative rate of complete cytogenetic response (CCyR) by 24 mo in older/younger pts was 70%/80% on BOS and 78%/80% on IM. Median time to CCyR was 24.0 wk for older versus 12.7 wk for younger pts on BOS and 24.4 wk versus 24.7 wk on IM; in younger pts CCyR was achieved significantly faster on BOS versus IM (P<0.001). Among older/younger pts with a CCyR, 57%/79% on BOS and 76%/85% on IM were still on treatment and retained their CCyR as of the data cutoff.

Cumulative rates of major molecular response (MMR) by 24 mo in older/younger pts were 53%/60% on BOS and 48%/49% on IM. Median time to MMR was 48.1 wk for older versus 48.0 wk for younger pts on BOS and 60.6 wk versus 84.1 wks on IM; for younger pts MMR was achieved significantly faster on BOS versus IM (P<0.001). Among older/younger pts with a MMR, 63%/84% on BOS and 92%/89% on IM were still on treatment and retained their MMR as of the data cutoff.

Kaplan-Meier event-free survival in older/younger pts at 2 y was 100%/91% on BOS and 81%/88% on IM. Kaplan-Meier on-treatment transformation to accelerated/blast phase CML by 2 y was 0% for older and 2% (4 transformations) for younger pts on BOS (4 total), and 9% (2 transformations) for older and 5% (11 transformations) for younger pts on IM (13 total). Kaplan-Meier overall survival in older/younger pts at 2 y was 100%/97% on BOS and 92%/95% on IM. The majority of deaths were due to disease progression (BOS, n = 6; IM, n = 10); few deaths due to AEs on BOS (n = 1) or IM (n = 2) were reported, none treatment related.

BOS was associated with higher rates of gastrointestinal TEAEs, elevated ALT and aspartate aminotransferase (AST), and pyrexia; IM was associated with higher rates of musculoskeletal TEAEs and edema (Table). Rates of common TEAEs were generally similar or higher among older pts. Pleural/pericardial effusion occurred in 6 (21%) older pts (3/6 with treatment-related events; median event duration, 36.5 d) versus 5 (2%) younger pts (all with treatment-related events) on BOS, and in no IM pts. Overall grade 3/4 TEAEs were more frequent among older pts on both BOS and IM, as was dose modification (Table).

Grade 3/4 lab abnormalities of elevated ALT (BOS, 18% older/24% younger; IM, 4% each) and AST (BOS, 7%/12%; IM, 4% each) were more frequent with BOS versus IM, but similar between age groups. Grade 3/4 lab abnormalities of neutropenia were more frequent with IM (23% older/22% younger) versus BOS (11% each) regardless of age; grade 3/4 anemia (6%-14%) and thrombocytopenia (14%-23%) were generally similar regardless of age or treatment arm.

In conclusion, BOS demonstrated activity in both older and younger pts with newly diagnosed CP CML. Although the frequency of certain toxicities as well as treatment discontinuations due to TEAEs was higher among older pts, the toxicity profile of BOS remained manageable and distinct from that of IM regardless of age.