What characterizes chronic myeloid leukemia (CML)?

• A. Malignancy of melanocytes in skin.
• B. Rapidly progressing cancer of lymphoid precursors.
• C. Myeloproliferative disorder associated with Philadelphia chromosome and excessive granulocyte production.
• D. Malignancy of plasma cells in bone marrow.

Answer: (C)

Chronic myeloid leukemia is a myeloproliferative disorder where the bone marrow makes too many myeloid cells, especially granulocytes. The defining feature is the Philadelphia chromosome, a t(9;22) translocation that creates the BCR-ABL fusion gene, which encodes a constitutively active tyrosine kinase. This drives uncontrolled proliferation and reduced cell death of granulocytic lineage cells, leading to marked leukocytosis with mature and maturing neutrophils and often basophilia, along with splenomegaly. It’s a myeloid, not lymphoid, cancer, and it involves granulocyte production rather than plasma cells or melanocytes. CML typically presents in a chronic phase and can progress if untreated, but it is highly responsive to targeted therapy that inhibits BCR-ABL, improving outcomes.