Peripheral Blood Neutrophil Nadir and Time to Platelet Recovery during Induction Chemotherapy: Predictors of Clinical Outcomes and Markers for Optimizing Induction Treatment Intensity in Acute Lymphoblastic Leukemia.

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To study the kinetics of blood count nadir and time to recovery and find its association with clinical outcomes in a cohort of Acute Lymphoblastic Leukemia (ALL). Data from 243 cases treated between January 2018 to December 2020 was retrospectively analysed. Along with baseline data, serial measures of peripheral blood counts, nadir, and time to partial and complete recovery of counts during course of induction chemotherapy were recorded. Post-induction Complete Remission (CR) status, Event-Free Survival (EFS) , and Overall Survival (OS) were recorded as clinical outcomes for analysis. Median age was 15 (range,1-62) years. Immunophenotype was B-ALL in 71% (n=172), and T-ALL in 27% (n=66). Good steroid response (D8) was seen in 89%(n=216), CR in 79% (n=192), and induction mortality in 12% (n=29). Median neutrophil nadir was 0.06(0-0.49) *10⁹/L and median day to nadir was D17. Median time to partial and complete platelet recovery was D18 and D25. Late neutrophil nadir (>D15) was independent predictor of refractory disease post-induction [OR=5.43 (95%CI 1.06-27.75)]. Late partial platelet recovery (>D22) was independent predictor of poorer EFS and OS [HR = 1.63 (95%CI 1.07-2.47)] and [HR = 1.5 (95% CI 1-2.4)] respectively. We found that a longer time to neutrophil nadir independently predicts refractory disease post-induction and late partial platelet recovery is an independent factor for poorer EFS and OS. Thus, Blood count kinetics as independent predictors of induction outcomes can provide a simple, easy-to-use tool for balancing toxicity-efficacy during induction therapy for ALL.