Mast cell leukemia (MCL) is the rarest and most aggressive form of systemic mastocytosis; approved targeted therapies are limited in Japan. We report a 63-year-old man with KIT D816V-negative MCL who presented with recurrent anaphylaxis and a high bone marrow mast cell burden. Cladribine produced hematologic improvement but did not control symptoms. Off-label dasatinib was used as bridging therapy and induced a partial response with resolution of symptoms. He subsequently underwent haploidentical allogeneic hematopoietic cell transplantation (allo-HCT) with reduced-intensity conditioning and post-transplant cyclophosphamide (PTCy)-based graft-versus-host disease (GVHD) prophylaxis. The early post-transplant course was complicated by sinusoidal obstruction syndrome (SOS), transplant-associated thrombotic microangiopathy (TA-TMA), infections, and cytokine release syndrome (CRS). Later, chronic hepatic GVHD (National Institutes of Health liver score 3) required treatment with ruxolitinib followed by belumosudil. Despite these complications, the patient has maintained complete remission for 33 months without maintenance therapy. This case suggests that dasatinib bridging followed by haploidentical allo-HCT with PTCy-based GVHD prophylaxis may be a feasible option for KIT D816V-negative MCL where approved tyrosine kinase inhibitors are unavailable. Early recognition and prompt management of transplant-related toxicities are critical.
Otani et al. (Thu,) studied this question.