Lineage switch in Philadelphia chromosome- positive acute lymphoblastic leukemia

BACKGROUND: An 8-year-old boy, initially diagnosed with Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) (French-American-British [FAB]-L1), relapsed with Ph+ acute myelogenous leukemia (AML) (FAB-M2) 21 months after successful ALL treatment with standard therapy. METHODS: The initial ALL presentation and subsequent AML relapse were analyzed by conventional morphologic, cytochemical, immunophenotypic, and cytogenetic studies. RESULTS: Molecular analysis based on the polymerase chain reaction identified the presence of a bcr-I-abl fusion transcript at initial ALL presentation, the completion of ALL therapy, and AML relapse. CONCLUSIONS: The cytogenetic and molecular results support a common clonal origin for this process. This is a case of lineage switch in a Ph+ acute leukemia. This case thus illustrates a manifestation of heterogeneous lineage differentiation among Ph+ acute leukemias.