Introduction. Hairy cell leukemia (HCL) is an uncommon B-cell lymphoproliferative disorder characterized by distinctive cells present in bone marrow, peripheral blood and spleen. Treatment of relapsed and/or refractory (R/R) HCL remains a challenge. Case report. A 28-year-old male was treated with cladribine +/- rituximab for his newly diagnosed BRAF-V600 mutated HCL. A year later leukemia relapsed and he received interferon alfa with poor response. Subsequently, vemurafenib was continued for 5 months but this treatment also failed. Then, he received bendamustine with rituximab but significant response was not achieved. Finally, he was found eligible for allogeneic stem cell transplantation (Allo-SCT) from a 9/10-matched unrelated donor. He was conditioned with total body irradiation (TBI) and cyclophosphamide. Cyclosporine and methotrexate were used as graft-versus-host prophylaxis (GVHD). He engrafted and achieved full donor chimerism. There were 0.4% of hairy cells in bone marrow sample by flow cytometry at discharge. 3 months after transplantation he developed neurological and psychiatric deficits which remained unexplained despite a detailed work-up. The symptoms partly resolved after steroids implementation. At the last contact, 14 months after transplantation he remained in complete remission and his neurological condition improved substantially. Conclusions. Allo-SCT seems to be a promising treatment option for R/R HCL.
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