Screening families with endometrial and colorectal cancers for germline mutations

Common variants in human CRC genes as low-risk alleles

The genetic susceptibility to colorectal cancer (CRC) has been estimated to be around 35% and yet high-penetrance germline mutations found so far explain less than 5% of all cases. Much of the remaining variations could be due to the co-inheritance of multiple low penetrant variants. The identification of all the susceptibility alleles could have public health relevance in the near future. To test the hypothesis that what are considered polymorphisms in human CRC genes could constitute low-risk alleles, we selected eight common SNPs for a pilot association study in 1785 cases and 1722 controls. One SNP, rs3219489:G>C (MUTYH Q324H) seemed to confer an increased risk of rectal cancer in homozygous status (OR=1.52; CI=1.06-2.17). When the analysis was restricted to our 'super-controls', healthy individuals with no family history for cancer, also rs1799977:A>G (MLH1 I219V) was associated with an increased risk in both colon and rectum patients with an odds ratio of 1.28 (CI=1.02-1.60) and 1.34 (CI=1.05-1.72), respectively (under the dominant model); while 2 SNPs, rs1800932:A>G (MSH6 P92P) and rs459552:T>A (APC D1822V) seemed to confer a protective effect. The latter, in particular showed an odds ratio of 0.76 (CI=0.60-0.97) among colon patients and 0.73 (CI=0.56-0.95) among rectal patients. In conclusion, our study suggests that common variants in human CRC genes could constitute low-risk alleles.

Colorectal cancer as a complex disease: defining at-risk subjects in the general population - a preventive strategy

Over the last few decades it has become clear that highly penetrant disease genes are responsible for a minor proportion of colorectal cancer cases. Families with hereditary syndromes are today recognized and included in surveillance programs known to reduce morbidity and mortality in colorectal cancer. Colorectal cancer is preventable and screening strategies in whole populations are currently under debate. Colorectal cancer can be considered a complex disease, with a combination of predisposing genetic variants and environmental factors that contribute to the illness as a whole. The progress made in the genome project provides an opportunity to determine such genetic variants and environmental factors. This knowledge can be used to define a subpopulation at increased risk for colorectal cancer. It will be more feasible to design preventive strategies for this subgroup than for a whole population.

Toward New Strategies to Select Young Endometrial Cancer Patients for Mismatch Repair Gene Mutation Analysis

Purpose: To determine the frequency of mismatch repair (MMR) gene germline mutations in endometrial cancer patients who were diagnosed at less than 50 years of age; to relate the presence of mutations to family history, histopathologic data, presence of tumor microsatellite instability (MSI), and immunostaining; and to formulate criteria for genetic testing in these patients.

Patients and Methods: Endometrial cancer patients (N = 58), who were diagnosed at less than 50 years of age, were included and questioned about their family history. Mutation analysis of the MLH1, MSH2, and MSH6 genes was performed (denaturing gradient gel electrophoresis and sequence analysis to detect small mutations and multiplex ligation-dependent probe amplification to detect large deletions or duplications). For MSI analysis, five consensus markers were used, and immunostaining of the three MMR proteins was performed.

Results: In five of 22 patients with a positive first-degree family history for hereditary nonpolyposis colorectal cancer (HNPCC)-related cancers, pathogenic germline mutations were found (one MLH1, three MSH2, and one MSH6). Four mutation carriers belonged to families fulfilling the revised Amsterdam criteria. No mutations were found in the 35 patients without such family history (P = .006). MSI was detected in 20 of 57 cancers, among which four were from mutation carriers. In 23 of 51 cancers, one or more MMR protein was absent; in all five mutation carriers, immunostaining indicated the involved MMR gene.

Conclusion: In 23% of the young endometrial cancer patients with at least one first-degree relative with an HNPCC-related cancer, an MMR gene mutation was detected. Therefore, presence of an HNPCC-related cancer in a first-degree relative seems to be an important selection criterion for mutation analysis. Subsequent immunostaining of MMR proteins will point to the gene(s) that should be analyzed.