The concise handbook of family cancer syndromes. Mayo Familial Cancer Program

Genetic testing in hereditary colorectal cancer: indications and procedures

Approximately 25% of colorectal cancers occur in younger individuals or those with a personal or family history of the disease, suggesting a heritable susceptibility. The minority of these cases are accounted for by one of the well-described hereditary colorectal cancer syndromes, familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC). The recent identification and cloning of the genes responsible for FAP and HNPCC, along with other colon cancer susceptibility genes, has led to the wide-spread availability of genetic testing for hereditary colorectal cancer. Genetic testing raises clinical, ethical, legal, and psychosocial questions that must urgently be discussed. This review highlights areas of knowledge and uncertainty about genetic predisposition testing for colorectal cancer and provides clinicians with practical recommendations regarding the proper indications and procedures for this testing.

Mismatch repair gene defects contribute to the genetic basis of double primary cancers of the colorectum and endometrium

Hereditary non-polyposis colorectal cancer (HNPCC) is a dominantly inherited cancer syndrome caused by germline defects of mismatch repair (MMR) genes. Endometrial cancer is the most common extracolonic neoplasm in HNPCC and is the primary clinical manifestation of the syndrome in some families. The cumulative incidence of endometrial cancer among HNPCC mutation carriers is high, estimated to be from 22 to 43%. We hypothesized that women with double primary cancers of the colorectum and endometrium are likely to be members of HNPCC families. In order to determine how frequently HNPCC manifests in the context of double primary cancers, we examined alterations of two MMR genes, hMSH2 and hMLH1, in 40 unrelated women affected with double primary cancers. These cases were identified using hospital-based and population-based cancer registries in Ontario, Canada. MMR gene mutations were screened by single-strand conformation polymorphism analysis and confirmed by direct sequencing. Eighteen percent (seven of 40) were found to harbor mutations of one of the two MMR genes. Analysis of colorectal and/or endometrial tumors of mutation-negative probands found microsatellite instability in seven of 20 cases. Six of seven mutation-positive probands had strong family histories suggestive of HNPCC. First degree relatives of mutation-positive probands had a very high relative risk (RR) of colorectal cancer (RR = 8.1, CI 3. 5-15.9) and endometrial cancer (RR = 23.8, CI 6.4-61.0). The relative risk of mutation-negative cases was 2.8 (CI 1.7-4.5) for colorectal cancer and 5.4 (CI 2.0-11.7) for endometrial cancer. We recommend that all double primary patients with cancers at these sites should have a genetic evaluation, including molecular analysis for HNPCC where appropriate.