Plasmablastic Myeloma- A Diagnostic Dilemma

Plasmablastic neoplasms comprise various haematolymphoid tumours with plasmablastic morphology which includes Plasmablastic Myeloma (PBM) and Plasmablastic Lymphoma (PBL). Distinguishing these two entities remains a major diagnostic challenge. In view of Epstein Barr Virus (EBV)-Encoded RNA (EBER) negativity, Human Immunodeficiency Virus (HIV) negativity, high Serum Free Light Chain (SFLC) assay and absence of hypermetabolic lymphadenopathy, a final diagnosis of PBM was made. This report is about a 55-year-old lady who presented with fatigue, significant loss of weight, and appetite. She had mild enlargement of the liver, spleen and no significant lymphadenopathy. There were atypical cells in peripheral blood. Bone marrow evaluation showed 51% atypical mononuclear cells. Flow cytometry was negative for acute leukaemia diagnostic markers. Immunohistochemistry (IHC) on the bone marrow biopsy revealed positivity for Cluster of Differentiation (CD) 138, Multiple Myeloma 1 (MUM1) with kappa light chain restriction and negative for EBER. The free light chain showed a kappa:lambda light chain ratio of 28,885 (0.26-1.65). The diagnosis of PBM was made and she was started on a daratumumab-based immunotherapy regimen. She achieved complete remission after induction with Measurable Residual Disease (MRD)