Immunologic and histologic studies were performed in 10 cases of myeloma that showed progression to a more aggressive proliferation, designated as immunoblastic sarcoma of B-cell type (B-IBS). Several patterns of clinical presentation were observed: eight patients showed typical multiple myeloma, four developed B-IBS within the bone marrow, and four developed B-IBS in multiple extramedullary sites; the remaining two patients had relatively localized myeloma, but also showed development of extramedullary B-IBS. The implications of these findings are discussed with regard to their prognostic import and their relationship to current concepts of plasma cell development.

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