Acute leukemia evolving from multiple myeloma and co‐expressing myeloid and plasma cell antigens

This report describes the development of acute myeloblastic leukemia in a patient after long‐term alkylator therapy for multiple myeloma. Despite chromosome deletions −5, −7, the patient lacked the histochemistry and clinical findings characteristic of therapy‐induced leukemia. In double‐labeled surface marker studies by flow cytometry, the leukemic blast cells co‐expressed myeloid and plasma cell surface markers. The findings may support the hypothesis of a single stem cell abnormality's being responsible for both the malignant plasma cells and the myeloid leukemic cells.