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T‐cell/histiocyte‐rich large B‐cell lymphoma – transformation of Nodular lymphocyte predominant Hodgkin lymphoma in the bone marrow

A 39-year-old Caucasian man presented with a history of fevers, weight loss, bone discomfort and polydipsia. He had previously received treatment for stage 2A Nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) in 2007 with four cycles of ABVD (Adriamycin, Bleomycin, Vinblastine, Dacarbazine) chemotherapy and local involved field radiotherapy to complete remission. He was pancytopenic (haemoglobin 9.7 g/dL, white cell count 2.39x10^9/L and platelet 110x10^9/L) and hypercalcaemic (corrected serum calcium was 3.30 mmol/L); renal and hepatic function were normal. A bone marrow aspirate wasn’t possible due to a dry tap so a trephine roll was performed in addition to the bone marrow trephine. This revealed a small population of large, pleomorphic, primitive cells with prominent nucleoli, a high nuclear to cytoplasmic ratio, and vacuolated basophilic cytoplasm admixed with a large infiltrate of small, mature lymphocytes Fig. 1 Given these characteristic changes and the patient’s previous history, a diagnosis of T-cell/histiocyte-rich large B-cell lymphoma (THR-LBCL) was suspected. Morphological and immunohistochemical analysis of the trephine confirmed this, demonstrating a 90% infiltration of reactive T cells (CD3 positive) admixed with small numbers of single, scattered large, pleomorphic, immature B cells (CD20 and CD79a positive and CD30 negative). A staging fluorodeoxyglucose-positron emission tomography (FDG-PET) CT of the neck, chest, abdomen and pelvis revealed extremely FDG-avid stage IV disease (SUV max 28.1) with extensive bone marrow involvement Fig. 2. The patient was initially treated with R-CHOP (Rituximab, Cyclophosphamide, Doxorubicin, Vincristine, and Prednisolone) with the aim to switch to salvage chemotherapy and perform autologous stem cell transplantation. This case represents an unusual presentation of a well described complication of NLPHL. THR-LBCL can develop synchronously or metachronously. The findings seen on the trephine roll were so distinctive that the diagnosis was