Bone Marrow Findings in Patients With Acute Promyelocytic Leukemia Treated With Arsenic Trioxide.

Objectives: Increasingly, acute promyelocytic leukemia (APL) is treated with a combination of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). This study characterizes bone marrow findings after ATRA/ATO therapy. Methods: Bone marrow biopsies from 16 patients treated with ATRA/ATO and seven patients treated with ATRA/chemotherapy (CTX) for APL were evaluated. Results: In ATRA/ATO cases, the marrow was likely to be hypercellular (79%) with a decreased myeloid:erythroid (M:E) ratio (88%), megaloblastoid maturation of erythroid precursors (100%), erythroid atypia (75%), and increased (88%) and atypical (75%) megakaryocytes. Significant myeloid atypia was only seen in extensive residual disease. The ATRA/CTX cases were less likely to be hypercellular (38%), have a M:E ratio of 1:1 or less (0%), exhibit significant erythroid atypia (0%), or have increased (0%) or atypical (38%) megakaryocytes. Conclusions: Bone marrow biopsies from patients treated with ATO have unusual but characteristic features. Despite variability in marrow findings, clinical outcomes were uniformly favorable.