Anaplastic large cell lymphoma (ALCL) with ALK gene rearrangement most commonly involves which chromosomal translocation, and what fusion protein does it produce?
- A t(2;3)(p23;q27) producing BCL6-ALK fusion
- B t(2;5)(p23;q35) producing NPM1-ALK fusion ✓
- C t(5;9)(q33;q22) producing ITK-SYK fusion
- D t(11;18)(q21;q21) producing API2-MALT1 fusion
Explanation
The classic translocation in ALK-positive ALCL is t(2;5)(p23;q35), which fuses the ALK gene on chromosome 2p23 with the NPM1 (nucleophosmin) gene on chromosome 5q35, producing the NPM1-ALK (p80) fusion protein. This fusion constitutively activates ALK tyrosine kinase via dimerization, driving cell proliferation through JAK-STAT3, PI3K/AKT, and MAPK pathways. ALK+ ALCL has better prognosis than ALK- ALCL. BCL6-ALK involves a rare variant translocation; ITK-SYK occurs in follicular helper T-cell lymphomas; API2-MALT1 is found in gastric MALT lymphoma — none are ALCL-specific.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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