Impact of colonoscopic screening in Familial Colorectal Cancer Type X

Background

Hereditary Non‐Polyposis Colorectal cancer is caused by Lynch Syndrome (LS; an autosomal dominant condition) or by Familial Colorectal Cancer Type‐X (FCCTX; a condition of high family risk that fulfills Amsterdam criteria). The lifetime risk of developing colorectal cancer (CRC) in FCCTX family members is high and CRC occurs later than in LS.

Methods

To determine the impact of primary prevention colonoscopic screening in asymptomatic first‐degree relatives of incident CRC cases in 20 families with FCCTX, we compared cancer incidence and survival in 79 males and 83 females, assumed to be at 50% risk of inheriting a genetic CRC susceptibility factor, who entered screening to an unscreened control group from the families, matched for age at entry into screening and for sex.

Results

In males, median age at entry into screening was 44.8 years, median follow‐up 12.4 years, 12% developed CRC, and 46% died after 30 years of follow‐up. Compared to the unscreened group, relative risk of CRC was 0.27 (95% confidence intervals (CI) 0.10–0.71). In screened females, comparable results were 44.5 years at entry, 11.2 years of follow‐up, 7.1% developed CRC, and 7.2% died after 30 years of follow‐up. The relative risk of CRC compared to the unscreened group was 0.19 (95% CI 0.07–0.48).

Conclusion

Primary prevention screening colonoscopy in asymptomatic family members significantly decreased the risk of CRC in FCCTX.

A population-based study of hereditary non-polyposis colorectal cancer: evidence of pathologic and genetic heterogeneity

Hereditary non-polyposis colorectal cancer (HNPCC) may be the result of Lynch syndrome (LS) caused by mutations in mismatch repair (MMR) genes, a syndrome of unknown etiology called familial colorectal cancer type-X (FCCTX), or familial serrated neoplasia associated with the colorectal cancer (CRC) somatic BRAF mutation. To determine the cause of HNPCC in the founder population of the island of Newfoundland, we studied 37 families with LS and 29 families without LS who fulfilled the Amsterdam I criteria. In non-LS, four index CRCs were BRAF mutation positive, one of which was microsatellite instable. Geographic clustering of LS families caused by three different founder mutations in MSH2 was observed. Nine unique MMR mutations in four MMR genes were identified in single families distributed in different geographic isolates. The geographic distribution of non-LS was similar to LS. The coefficient of relatedness using genotype data was significantly higher for non-LS than for all CRC. Extensive genealogic investigation failed to connect non-LS families and in some clusters pathologic CRC heterogeneity was observed. We conclude that non-LS HNPCC may be a heterogeneous disorder with different pathogenic pathways, and that the geographic distribution is consistent with multiple different mutations in unknown CRC susceptibility gene(s).

Genomic instability and carcinogenesis: an update

Cancers arise as a result of stepwise accumulation of mutations which may occur at the nucleotide level and/or the gross chromosomal level. Many cancers particularly those of the colon display a form of genomic instability which may facilitate and speed up tumor initiation and development. In few instances, a "mutator mutation" has been clearly implicated in driving the accumulation of other carcinogenic mutations. For example, the post-replicative DNA mismatch repair deficiency results in dramatic increase in insertion/deletion mutations giving rise to the microsatellite instability (MSI) phenotype and may predispose to a spectrum of tumours when it occurs in the germline. Although many sporadic cancers show multiple mutations suggesting unstable genome, the role of this instability in carcinogenesis, as opposed to the power of natural selection, has been a matter of controversy. This review gives an update of the latest data on these issues particularly recent data from genome-wide, high throughput techniques as well as mathematical modelling. Throughout this review, reference will be made to the relevance of genomic instability to the pathogenesis of colorectal carcinoma particularly its hereditary and familial subsets.