[Aggressive non-nodal mantle cell lymphoma with challenging subtype classification at presentation].

A 57-year-old man presented with neutropenia, circulating blast-like cells, anemia, and fever. Bone marrow examination revealed that 62.8% of nucleated cells were small lymphoid blast-like cells, whose surface markers and immunophenotype were consistent with mantle cell lymphoma (MCL). Because no nodal involvement was detected at the initial visit, leukemic non-nodal MCL (nnMCL) was initially considered. However, 18F-fluorodeoxyglucose positron emission tomography demonstrated diffuse bone uptake and new nodal lesions that had not been apparent at presentation. The presence of SOX11 positivity, a high Ki-67 index, a complex karyotype, and the rapidly progressive clinical course were atypical for nnMCL and instead resembled conventional MCL. Although differentiation was challenging, a treatment protocol for aggressive conventional MCL was followed. The patient received bendamustine and rituximab, followed by CHASE-R (cyclophosphamide, cytarabine, dexamethasone, etoposide, and rituximab), and then high-dose chemotherapy with autologous peripheral blood stem cell transplantation. This case was considered borderline between conventional MCL and nnMCL. Although a definitive classification was not made, the treatment strategy was determined based on the pathological features, chromosomal abnormalities, and clinical behavior, following the approach typically used for aggressive conventional MCL.