[Allogeneic stem cell transplantation for aggressive NK cell leukemia]

Aggressive NK cell leukemia (ANKL) is a rare leukemic form of mature NK cell neoplasms. ANKL presents a fulminant clinical course with a median overall survival (OS) of 2-3 months after diagnosis. Currently, allogeneic stem cell transplantation (allo-HSCT) is the only curative treatment for ANKL patients. Although a few recent reports have evaluated the efficacy of allo-HSCT for ANKL patients, detailed outcomes of allo-HSCT are obscure. We conducted a nationwide retrospective analysis of 59 ANKL patients who underwent first allo-HSCT between 1997 and 2016 in Japan. The median age was 37 years, and 68% were male. The 1- and 5-year OS were 33.9% and 27.3%, respectively; the 1-year cumulative incidence of relapse or progression was 55.5%. The OS was significantly better for patients with complete or partial responses as the time of allo-HSCT, which was equivalent to that for patients who experienced primary induction failure but achieved complete response after allo-HSCT. Patients who underwent cord blood transplantation had significantly better outcomes than those who underwent allo-HSCT from other sources. Therefore, our study demonstrates that allo-HSCT is a promising treatment that can provide a durable response in a subset of ANKL patients. A larger-scale study including unselected ANKL patients is warranted in the future.