Acute Promyelocytic Leukemia with <b><i>Flt3-TKD</i></b> and <b><i>WT1</i></b> Mutations Relapsing in a Testicle and Followed by Systemic Relapse

Extramedullary relapse is a rare phenomenon in patients with acute promyelocytic leukemia (APL), especially that derived from urogenital systems like the testicles. In this report, we describe an APL patient who had received standard induction/maintenance therapy resulting in durable remission for 4.5 years, when he presented with a unilateral testicular mass confirmed as myeloid sarcoma; this was followed by systemic relapse of APL. Retrospective analysis of the involved blood and bone marrow samples at the time of the initial diagnosis revealed a rare point mutation of FLT3-TKD and a novel mutation of WT1. These mutations were detected recurrently throughout the course of the disease. After reinduction therapy with arsenic trioxide and all-trans retinoic acid combined with daunorubicin, complete hematological remission was achieved for the ensuing salvage allogeneic hematopoietic stem cell transplant.