Persistent monotypic plasma cells with absence of neoplastic B cell component in a treated case of waldenström macroglobulinemia: a sign of residual disease?

Waldenström macroglobulinemia (WM) is a rare indolent variant of non- Hodgkin's lymphoma characterised by lymphoplasmacytic infiltration of bone marrow (BM) associated with a serum IgM paraprotein. The WHO classification states that the neoplastic cells of WM usually are positive for monotypic surface immunoglobulin light chain, IgM, CD19, and CD20 and are negative for CD5, CD10, and CD23. Serum monoclonal protein detection by serum protein electrophoresis and bone marrow aspirate and biopsy are required for WM diagnosis, monitoring and response assessment. Pathologist must dissuade themselves from making a hasty decision on calling a complete response in WM when neoplastic B cell component is absent. Evaluation of clonality of any residual plasma cells must be done in all cases of WM to evaluate the presence and extent of residual or persistent disease. Role of additional therapy targeted at these residual plasma cells in WM can be evaluated as tools for achieving complete remission. Herein, we present a case of WM with residual monotypic plasmacytosis in BM, without B lymphocytes after therapy.