Double leukemias simultaneously showing lymphoblastic leukemia of the bone marrow and monocytic leukemia of the central nervous system.

A rare case of different leukemias simultaneously occurring in the bone marrow (BM) and the central nervous system (CNS) was encountered. A 4-year-old girl was diagnosed with acute lymphoblastic leukemia and achieved a complete remission with chemotherapy. Two years after diagnosis, she was found to have acute monocytic leukemia at first relapse in the BM. One month after the second course of induction therapy, lymphoblastic leukemia in the BM and monocytic leukemia in the CNS were found simultaneously. Chromosomal analysis of leukemia cells in the BM and CNS showed distinct results. The mechanism of double leukemias occurring was obscure, although a lineage switch, therapy-related, or de novo leukemia could be considered as possibilities. Double leukemias should be kept in mind when leukemias relapse in several sites.