Genetics of Colorectal Cancer (PDQ®): Genetics - Health Professional Information [NCI] - Major Genetic Syndromes
Table 8. Clinical Practice Guidelines for Diagnosis and Colon Surveillance of Familial Adenomatous Polyposis (FAP) continued...
The model predicted that if all endometrial cancers in the United States (estimated to be 45,000 new cases in 2010) underwent IHC screening, 827 women (1.84%) would be diagnosed as LS patients. However, applying the strategy of testing only those endometrial tumors of patients with at least a first-degree relative with LS-related cancer, 755 affected individuals (1.68%) would be identified. If the Amsterdam II criteria were applied, 539 carriers (1.2%) would be identified. The authors stated that the incremental benefit of the most cost-effective strategy was only associated with an average life expectancy gain of 1 day compared with testing by Amsterdam II criteria. However, they argue that this may be significant, as it is comparable to the life expectancy gain from triennial cervical cancer screening, which is a current recommendation from the American College of Obstetricians and Gynecologists for women older than 30 years in the general population.
Several aspects of the biologic behavior of LS suggest how the approach to surveillance should differ from that for average-risk people:
- CRCs in LS occur earlier in life than do sporadic cancers. For MLH1 and MSH2 mutation carriers, the estimated risk of CRC at age 40 years is 31% for females and 32% for males; at age 50 years, the estimated risks are 52% and 57%, respectively. This suggests that screening should begin earlier in life.
- A larger proportion of LS CRCs (60%–70%) occur in the right colon, suggesting that sigmoidoscopy alone is not an appropriate screening strategy and that a colonoscopy provides a more complete structural examination of the colon. Annual colonoscopic surveillance is recommended.
- The progression from normal mucosa to adenoma to cancer is accelerated,[316,317] suggesting that screening should be done at shorter intervals (every 1–2 years) and with colonoscopy.[317,318] Because patients with LS have an ordinary, or slightly increased, frequency of polyps but a substantially increased rate of cancer, it is clear that a larger proportion of polyps progress to cancer. It has been demonstrated that MMR gene mutation carriers develop adenomas at an earlier age than noncarriers. The mean age at diagnosis of adenoma in carriers was 43.3 years (range, 23–63.2 years), and the mean age at diagnosis of carcinoma was 45.8 years (range, 25.2–57.6 years).
- Incidence of CRC through life is substantially higher, suggesting that the most sensitive test available should be used.
- Patients with LS are at an increased risk of other cancers, especially those of the endometrium and ovary. The cumulative risk of extracolonic cancer has been estimated to be 20% by age 70 years in 1,018 women in 86 families, compared with 3% in the general population. There is some evidence that the rate of individual cancers varies from kindred to kindred.[220,319,320] Expert consensus suggests consideration of endometrial cancer screening by age 25 years.