Screening Decisions in a Family With a Germline Mutation
A 45-year-old man undergoes colonoscopy for iron-deficiency anemia. A 3-cm sessile serrated lesion with dysplasia is removed piecemeal from the ascending colon, and two additional 6-mm hyperplastic polyps are found. His mother had colon cancer at 52 and his maternal uncle at 48; a cousin recently tested positive for a pathogenic MLH1 germline mutation. The patient's tumor shows loss of MLH1 and PMS2 on immunohistochemistry with BRAF V600E wild-type. Genetic counseling is arranged, but he asks whether he can just get 'checked every few years like everyone else.'
1. Interpret the immunohistochemistry and BRAF result. Does this represent Lynch syndrome, and what testing confirms it?
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IHC showing loss of MLH1 and PMS2 indicates mismatch repair deficiency. Because MLH1 and PMS2 form a heterodimer in which MLH1 is the obligatory partner, loss of MLH1 protein causes secondary loss of PMS2 - so the paired loss points to an MLH1 abnormality rather than isolated PMS2 loss.
The BRAF V600E result is the key discriminator. BRAF V600E mutations are present in the majority of sporadic MLH1-deficient tumors (via the CpG island methylator pathway, often with MLH1 promoter hypermethylation) and are essentially absent in Lynch syndrome. Here BRAF V600E is wild-type (negative), which argues against a sporadic MLH1-methylation cause and raises suspicion for Lynch syndrome.
Confirmation:
- MLH1 promoter hypermethylation testing on tumor tissue - if positive, supports sporadic origin; if negative, strongly supports Lynch.
- Germline testing of MLH1 (and the MMR panel) - this is the definitive test. Given the family history and a known familial MLH1 mutation, targeted testing for that variant is efficient.
- Note: this patient's index lesion is a serrated lesion; the tumor tested should be the dysplastic/cancerous tissue, and results must be interpreted with the family history.
Conclusion: this is not a 'screen like everyone else' situation - the combination of family history, MMR loss, and BRAF wild-type status makes Lynch syndrome likely until germline testing says otherwise.
2. Assuming Lynch syndrome is confirmed, specify his surveillance plan and the surveillance/counseling implications for his relatives.
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His surveillance (Lynch syndrome, MLH1):
- Colonoscopy every 1–2 years, beginning at age 20–25 (or 2–5 years before the earliest family diagnosis, whichever is earlier). He is already 45 and has had an advanced lesion, so annual or every-1–2-year intervals are appropriate; the piecemeal removal of a 3-cm lesion warrants a surveillance colonoscopy in 3–6 months to confirm complete resection before settling into the interval schedule.
- Upper endoscopy for gastric/duodenal cancer surveillance is recommended in some Lynch kindreds (particularly Asian populations); at minimum, consider it and treat H. pylori.
- Urinary tract surveillance for urothelial cancer (especially with MSH2/MSH6); urinalysis/cytology annually is reasonable.
- Gynecologic surveillance does not apply to him, but is relevant for female relatives.
- Aspirin chemoprevention - evidence (CAPP2) supports aspirin 600 mg daily reducing Lynch-associated colorectal cancer; discuss with him.
- Endometrial/ovarian risk-reducing surgery counseling for female carriers.
Relatives:
- First-degree relatives should undergo genetic counseling and cascade testing for the known MLH1 variant. Carriers → intensive surveillance as above; non-carriers → average-risk screening.
- Because the mutation is known in a cousin, targeted single-site testing is inexpensive and definitive.
- Emphasize that Lynch surveillance reduces colorectal cancer incidence and mortality - this is not optional screening.
3. He asks whether his serrated lesion changes anything compared with 'regular polyps.' How do you counsel him on serrated pathway biology and post-polypectomy follow-up?
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Serrated pathway biology: sessile serrated lesions (SSLs) are precursors in the serrated neoplasia pathway, driven by BRAF mutation and CpG island methylation, and can progress to cancer via MLH1 promoter hypermethylation (sporadic) or, in his case, germline MMR loss. They are often right-sided, flat, mucus-capped, and harder to detect - which is why high-quality bowel prep and careful inspection of the right colon matter.
His specific lesion: a 3-cm SSL with dysplasia is an advanced lesion. Piecemeal resection of a large SSL carries a meaningful risk of incomplete resection and recurrence, so:
- Repeat colonoscopy at 3–6 months to inspect the resection site (and consider endoscopic marking/tattoo at the index procedure).
- If residual tissue is found, consider endoscopic mucosal resection or ESD rather than repeat piecemeal snaring.
General post-polypectomy guidance: for an advanced serrated lesion, surveillance intervals are shortened (roughly 3 years in average-risk patients per US and European guidance), but his Lynch diagnosis overrides the generic schedule and drives 1–2-year intervals.
Counseling points: (1) serrated lesions are not 'harmless hyperplastic polyps' when large or dysplastic; (2) his diagnosis changes both his interval and his relatives' care; (3) adherence to surveillance is the single biggest modifiable factor in his outcome.