Erythroblastic transformation of Philadelphia chromosome (Ph1)-positive chronic myelogenous leukemia associated with marked chromosomal rearrangements.

In a 22-year-old female with Philadelphia chromosome (Ph1)-positive chronic myelogenous leukemia (CML) a tumor consisting of megaloblastic proerythroblasts appeared in the right ilio-femoral region 2 years and 8 months after the diagnosis of the disease and was treated effectively with irradiation. She developed erythroblastic transformation 3 months after the tumor appeared. Cytogenetic study of the bone marrow cells in the acute phase revealed marked chromosomal rearrangements such as ring, dicentric, or tricentric chromosomes.