A 52-year-old man with colorectal cancer has a tumour showing loss of MLH1 expression on immunohistochemistry and high-frequency microsatellite instability. Which hereditary syndrome must be excluded in him and his relatives?
- A Familial adenomatous polyposis
- B MUTYH-associated polyposis
- C Lynch syndrome ✓
- D Peutz-Jeghers syndrome
Correct answer: C. Lynch syndrome
Explanation
Lynch syndrome arises from germline mutations in DNA mismatch repair genes, chiefly MLH1, MSH2, MSH6, and PMS2. Defective repair produces microsatellite instability, detectable as high-frequency MSI or loss of the corresponding protein on immunohistochemistry. Familial adenomatous polyposis and MUTYH-associated polyposis follow APC and MUTYH defects respectively with chromosomal instability, and Peutz-Jeghers involves STK11, none of which produce microsatellite instability.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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