A 35-year-old patient is found to have Philadelphia chromosome t(9;22). The resulting BCR-ABL1 fusion protein has constitutively active kinase activity. In chronic phase CML, which cell lineage is predominantly expanded?

• A Myeloid progenitors capable of full maturation ✓
• B Lymphoid progenitors arrested at pre-B stage
• C Erythroid progenitors with megaloblastic change
• D Megakaryocytes with defective platelet production

Explanation

In chronic phase CML, BCR-ABL1 drives proliferation of myeloid progenitors that retain the ability to mature, resulting in a full spectrum of myeloid cells (neutrophils, eosinophils, basophils, monocytes) in the peripheral blood. The blast crisis represents failure of differentiation. Lymphoid expansion is seen in ALL. Megaloblastic changes are not characteristic.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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