Chronic myelogenous leukemia with p190BCR-ABL expression: the missing link with monocytosis.

Chronic myelogenous leukemia (CML) is a clonal myeloproliferative disorder, which involves myeloid, monocytic, erythroid, megakaryocytic, B-lymphoid, and occasionally Tlymphoid lineages. It was the first human disease in which a specific abnormality of karyotype the Philadelphia (Ph) chromosome, t(9;22)(q34;qll) translocation could be linked to pathogenetic events of leukemogenesis. The BCR-ABLhybrid gene, the product of the Ph chromosome, is found in the leukemic clone of at least 95% of CMLpatients diagnosed by conventional clinical features. The fusion protein encoded by BCRABLvaries in size, depending on the breakpoint in the BCR gene. Three breakpoint cluster regions have been characterized to date: major (M-bcr), minor (m-bcr) and micro (|i-bcr) (1).