A 58-year-old man is found on routine CBC to have a WBC of 85,000/µL with a differential showing neutrophils at all stages of maturation, basophilia, and <2% blasts. Spleen is massively enlarged. BCR-ABL1 is detected by FISH. Which of the following best explains the massive splenomegaly in this condition?

• A Extramedullary hematopoiesis replacing splenic white pulp
• B Splenic sequestration of destroyed platelets causing reactive hyperplasia
• C Leukemic infiltration and extramedullary hematopoiesis in the red pulp ✓
• D T-cell lymphoma involving marginal zone

Explanation

In CML, the BCR-ABL1 fusion drives clonal proliferation of myeloid cells that infiltrate the splenic red pulp and also establish extramedullary hematopoiesis there, producing the massive splenomegaly characteristic of chronic phase. The red pulp sinusoids are expanded by granulocytic cells at all maturation stages. This is distinct from reactive splenomegaly (white pulp hyperplasia) and from lymphomatous involvement of the marginal zone.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.