[Secondary myeloid/natural killer cell acute leukemia appeared in multiple myeloma treated with melphalan]

A 67-year-old woman was treated with MP-P therapy and combination chemotherapy for multiple myeloma IgG-lambda type. After the therapy for about three years, pancytopenia developed. Bone marrow aspiration study revealed a few of myeloma cell and many atypical cells showing promyelocytic feature. Chromosomal abnormality was 46, X, -X, +8, -13, +mar. CD33 and CD56 were positive, but CD16 and HLA-DR were negative. We diagnosed as multiple myeloma complicated with secondary myeloid/natural killer (NK) cell acute leukemia. After she had been treated with low dose etoposide for leukemia, she obtained complete remission. But since myeloma progressed and the amount of M protein was increased, she was treated with dexamethasone and low dose etoposide, resulting in a decrease in the amount of M protein. After that, because of leukemic cell re-proliferation, she was treated with etoposide. However, she died of sepsis due to severe myelosuppression. This case was interesting one in coexist of multiple myeloma and secondary myeloid/NK cell acute leukemia, and those affecting her clinical course each other.