A test reveals the Philadelphia chromosome. Which disease is this chromosome most commonly associated with?

• A. Acute lymphoblastic leukemia
• B. Chronic myelogenous leukemia
• C. Hairy cell leukemia
• D. Acute myeloid leukemia

Answer: (B)

The Philadelphia chromosome is a t(9;22) translocation that creates the BCR-ABL fusion gene, which drives constitutive tyrosine kinase activity and unchecked myeloid cell proliferation. This abnormality is most classically linked to chronic myelogenous leukemia, and its presence is a hallmark diagnostic feature of CML. While this translocation can appear in some cases of adult acute lymphoblastic leukemia, it is far less common there, and hairy cell leukemia or acute myeloid leukemia are not typically associated with it. Recognizing this translocation is important because therapies targeting BCR-ABL, such as tyrosine kinase inhibitors, have dramatically improved outcomes in CML.