Successful autologous stem cell transplantation in a case of central nervous system relapse of diffuse large B-cell lymphoma with concurrent polycythemia vera.

Diffuse large B-cell lymphoma (DLBCL) with central nervous system (CNS) relapse is associated with a poor prognosis, and treatment becomes particularly challenging in such cases when complicated by polycythemia vera (PV). We report a unique case of CNS-relapsed DLBCL coexisting with PV, successfully treated with autologous stem cell transplantation (ASCT). A 64-year-old man achieved complete remission following R-CHOP therapy for DLBCL but developed isolated CNS relapse one year later. After achieving partial remission with high-dose methotrexate, he was referred for ASCT. On admission, erythrocytosis prompted further evaluation, leading to a diagnosis of JAK2 V617F-positive PV with an allele burden of 37.7%. Following phlebotomy, peripheral blood stem cells were successfully mobilized using reduced-dose G-CSF and plerixafor. ASCT was performed using a conditioning regimen of busulfan and thiotepa. Neutrophil engraftment occurred by day 10 without major adverse events. At 30 months post-ASCT, the patient remains in complete remission, with stable hemoglobin levels, a reduced JAK2 V617F allele burden (~ 12%), and no need for further phlebotomy. This case highlights the feasibility and potential dual therapeutic benefit of thiotepa-based ASCT in patients with coexisting CNS-relapsed DLBCL and PV. To our knowledge, this is the first reported case of ASCT in this clinical context.