Adults with Philadelphia Chromosome–Like Acute Lymphoblastic Leukemia: Considerations for Allogeneic Hematopoietic Cell Transplantation in First Complete Remission

Abstract

Philadelphia chromosome–like (Ph-like) acute lymphoblastic leukemia (ALL) is a subset of high-risk B cell ALLs. A large proportion of Ph-like ALL cases carry activating kinase mutations that could potentially allow them to be targeted by tyrosine kinase inhibitors. Ph-like ALL is not an uncommon entity, especially among adults, with a frequency exceeding 20%, including in older patients (>60 years old) with ALL. Ph-like ALL is associated with inferior outcomes across all ages, and studies have consistently shown a higher incidence of persistent postinduction minimal residual disease in patients carrying Ph-like ALL compared with other subgroups of ALL, and this translates into inferior leukemia-related outcomes. The inferior outcome of conventional chemotherapy for Ph-like ALL in adults raises the fundamental question of whether all adults with Ph-like ALL require an allogeneic hematopoietic cell transplantation (HCT) in first complete remission (CR1) regardless of other presenting features and treatment response parameters. Here we present and discuss several scenarios in which adults with Ph-like ALL underwent or were considered for HCT in CR1 for various reasons. Although the decision to proceed with HCT was clear and indisputable in some of these situations, in others we struggled with the decision to transplant in CR1 because of the lack of published data regarding the efficacy of allogeneic HCT as consolidation for Ph-like ALL. We emphasize the urgent need for developing well-designed studies to address this important question.