Which leukemia is most commonly associated with the Philadelphia chromosome?

• A. Hairy cell leukemia
• B. Acute lymphocytic leukemia
• C. Acute myelocytic leukemia
• D. Chronic myelogenous leukemia

Answer: (D)

The Philadelphia chromosome arises from a translocation between chromosomes 9 and 22, creating the BCR-ABL fusion gene. This fusion produces a constitutively active tyrosine kinase that drives uncontrolled proliferation of myeloid cells. That persistent signaling is most characteristic of chronic myelogenous leukemia, making it the leukemia most commonly associated with this chromosomal change. While some adult acute lymphoblastic leukemia cases can also harbor BCR-ABL, the classic association is with CML. Hairy cell leukemia is a different B-cell neoplasm with distinct features, and acute myeloid leukemia typically involves other cytogenetic abnormalities. Detecting BCR-ABL is clinically important because targeted therapy with tyrosine kinase inhibitors, like imatinib, can be highly effective.