LINEAGE SWITCH IN PHILADELPHIA-CHROMOSOME-POSITIVE ACUTE LYMPHOBLASTIC-LEUKEMIA

Background. An 8-year-old boy, initially diagnosed with Philadelphia c hromosome-positive (Ph(+)) acute lymphoblastic leukemia (ALL) (French- American-British [FAB]-L1), relapsed with Ph(+) acute myelogenous leuk emia (AML) (FAB-M2) 21 months after successful ALL treatment with stan dard therapy. Methods. The initial ALL presentation and subsequent AML relapse were analyzed by conventional morphologic, cytochemical, immu nophenotypic, and cytogenetic studies. Results. Molecular analysis bas ed 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 molecul ar results support a common clonal origin for this process. This is a case of lineage switch in a Ph(+) acute leukemia. This case thus illus trates a manifestation of heterogeneous lineage differentiation among Ph(+) acute leukemias.