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...
Evidence-based reviews of surveillance colonoscopy in LS have been reported.[350,351] There is only one controlled trial of CRC screening in LS.[345,346] In a study from Finland, 252 at-risk members of 22 families with LS were offered screening for 15 years. One hundred thirty-three individuals accepted screening by either colonoscopy or barium enema and sigmoidoscopy, and 123 of the at-risk members (93%) completed screening. One hundred nineteen did not accept advice to be screened, although 24 (20%) had screening examinations outside the study. Once genetic testing was performed in these families (starting in 1996, 14 years after the beginning of screening), screening was recommended for mutation-positive controls, 63% of whom chose to begin active screening. The screened group had 62% fewer cancers (P < .03) and 65% fewer CRC deaths (10 vs. 26, P = .003). All of the CRCs detected in the screened population were local and caused no deaths, compared with nine deaths from CRC in the control group. The results, while biologically plausible, are of limited validity, primarily because the main comparison was between compliant and noncompliant patients, and compliant patients have been shown to have an inherently better prognosis, independent of intervention. This assertion is supported by the observed low rates of all causes of mortality. It is noteworthy, however, that these differences were observed in spite of the fact that most mutation-positive controls ultimately entered a screening program.
The data from this Finnish trial were subsequently updated. Over the course of the study (early 1980s to present), the approach to colonoscopy surveillance has evolved. Colonoscopy was the approach used for MMR mutation carriers when this information was obtainable and the interval between exams was shortened from 5 years to 3 years to 2 years. The series limited its attention to subjects with no prior diagnosis of adenoma or cancer. The 420 mutation carriers, at a mean age of 36 years, underwent an average of 2.1 colonoscopies, with a median follow-up of 6.7 years. Adenomas were detected in 28% of subjects. Cumulative risk of one or more adenomas by age 60 years was 68.5% in men and 48.3% in women. Notably, risk of detecting cancer in those free of cancer at baseline exam, and thus regarded as interval cancers, by age 60 years was 34.6% in men and 22.1% in women. The combined cumulative risk of adenoma or cancer by age 60 years was 81.8% in men and 62.9% in women. For both adenomas and carcinomas, about half were located proximal to the splenic flexure. While the rates for CRC despite colonoscopy surveillance appear high, it must be emphasized that the recommended short intervals were not regularly adhered to in this nonrandomized series. These authors concluded by recommending surveillance at 2-year intervals. The appropriate colonoscopy surveillance interval remains every 1 to 2 years according to most consensus guidelines (see Table 9). Analysis of surveillance data in 242 patients 10 years after mutation testing shows 95% compliance in surveillance procedures for CRC and endometrial cancer. Although not all CRCs were prevented, mortality was comparable with mutation-negative relatives. However, this may be attributable to the modest sample size of the study.