A peripheral blood smear from a 35-year-old shows lymphocytes with condensed chromatin, round nuclei, and scanty cytoplasm. Flow cytometry reveals CD19+, CD5+, CD23−, FMC7+, CD10−, cyclin D1+. FISH shows t(11;14)(q13;q32). This translocation juxtaposes CCND1 with which genetic element?
- A MYC oncogene promoter
- B IGH (immunoglobulin heavy chain locus) enhancer ✓
- C BCL-2 promoter
- D TCR alpha chain enhancer
Correct answer: B. IGH (immunoglobulin heavy chain locus) enhancer
Explanation
In mantle cell lymphoma (MCL), the t(11;14)(q13;q32) translocation juxtaposes the CCND1 gene (encoding cyclin D1) on chromosome 11 with the immunoglobulin heavy chain (IGH) locus enhancer on chromosome 14. This places CCND1 under the control of the strong IGH enhancer, causing constitutive overexpression of cyclin D1, which drives cells through the G1/S cell cycle checkpoint by phosphorylating and inactivating Rb. The classic MCL immunophenotype is CD5+, CD23−, cyclin D1+ confirming this diagnosis.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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