Philadelphia chromosome
Chapter: 20b
Characteristic cytogenetic abnormality associated with CML and some cases of acute leukemia. Philadelphia chromosome results from a reciprocal translocation between chromosomes 9 and 22 [ t(9;22)(q34;q11)]. The molecular changes involve the translocation of the abl oncogene on chromosome 9 to the major breakpoint cluster region on chromosome 22, with production of the bcr/abl hybrid gene. In CML, the Philadelphia chromosome is present in all cells of the myeloid lineage, including neutrophils, erythroblasts, megakaryocytes, monocytes, eosinophils and basophils.