Biclonal chromosome evolution of chronic myelomonocytic leukemia in a child.

A monosomy 7 was first detected in a 6-month-old boy with a chronic myelomonocytic leukemia. After etoposide treatment, relapse occurred after 29 months, with transformation of the disease into an acute myeloblastic leukemia. After bone marrow transplantations, two abnormal clones were found in marrow cells: 45,XY,-7,del(12)(p11p12)(66%), and 45,XY,-7,t(3;12)(q26;p12)(33%). Several karyotypic studies performed until the terminal phase exhibited the persistence of these two clones in the same proportion, although both independently acquired additional and often similar anomalies. The clone with t(3;12) acquired der(7),der(11),der(17),der(8),der(10),-5,-20, and the clone with del(12p), del(5q),der(4),der(8),der(10),der(17),-5,-20. The anomalies in 12p12 appear to represent an important although secondary event of the neoplastic process. The other anomalies may correspond to either those of a secondary acute nonlymphocytic leukemia, since they occurred after treatment by etoposide and alkylating agents, or to the natural evolution of myelomonocytic leukemia.