Timing matters: Impact of covalent BTK inhibitor dose modifications on outcomes in chronic lymphocytic leukemia/small lymphocytic leukemia-A 7-year real-world study.
BACKGROUND: Covalent BTK inhibitors (cBTKis) are the cornerstone of chronic lymphocytic leukemia (CLL)/small lymphocytic leukemia (SLL) therapy, yet real-world data on dose modifications and their differential impact on long-term outcomes remain incompletely defined. This study investigated the incidence, timing, and the effectiveness of drug switching in a real-world CLL cohort. METHODS: In this 7-year retrospective real-world study, 324 CLL/SLL patients treated at a specialized Shanghai outpatient clinic (April 2018-April 2025; median follow-up, 42 months) were analyzed. Dose modifications were classified as dose interruption (DI) or dose reduction (DR). Their prognostic impact on progression-free (PFS) and overall survival (OS) was assessed by Kaplan-Meier analysis and multivariate Cox regression. RESULTS: The 42-month PFS rate was 70.2%. Of 324 patients, 229 (70.7%) experienced dose reductions or interruptions; infections were the predominant cause (61.9%). The full-dose (FD) group (n = 90) demonstrated superior 4-year PFS (93% vs. 58%, p < .001) and OS (98% vs. 76%, p = .007). Early modifications (0-3 months) were independent predictors of inferior PFS (hazard ratio [HR], 3.93, p = .008) and OS (HR, 3.29, p = .014). Prolonged DI (>14 days) was associated with inferior PFS (HR, 2.64) and OS (HR, 2.15), whereas DR and short DI (≤14 days) had negligible impact. Early (0-3 months) prolonged DI was devastating (3-year PFS, 41.2%; HR, 3.84, p < .001). cBTKi switching (n = 82; 100% nonprogression-driven) shortened DI (median, 6 vs. 14 days) and was independently associated with superior OS (HR, 0.34, p = .018) and PFS (HR, 0.36, p = .022). CONCLUSIONS: Early prolonged DI is the dominant adverse prognostic factor in cBTKi-treated CLL/SLL. Proactive switching minimizes treatment gaps and improves survival, supporting a timing-aware, DI- versus DR-informed approach to dose management.