Genetic counselling and consent for tumour testing in HNPCC

Molecular pathological tests are performed on stored tumour material in order to identify individuals with hereditary non-polyposis colorectal cancer. We have previously identified that there is widespread use of this testing and now describe what counselling occurs prior to testing and the approaches in seeking consent. A respondent from every cancer genetic centre in UK offering microsatellite instability and/or immunohistochemistry testing (n= 20, response rate = 100%) was interviewed in order to ascertain pre-test counselling and consent protocols. Individuals providing consent are not always seen in person prior to providing consent but few services had supporting written information. Nine (of 19) consent forms documented consent to perform genetic testing, while the majority (14/19) sought consent to release pathology samples to the genetic service. Less than half of the services routinely seek consent to test samples from a deceased individual. Concerns were raised about spousal consent when the implications of results are for blood relatives. The differences identified between genetic counselling for testing of tumour tissue and for germ-line genetic testing suggest that counselling protocols specific for somatic testing should be developed. The results are discussed in the context of a changing legal environment and anticipated growing demand for testing.

Variability and inequity in testing of somatic tissue for hereditary cancer: a survey of UK clinical practice

A growing body of literature demonstrates the benefits of molecular pathological investigations of tumour material in the identification of individuals with hereditary non-polyposis colorectal cancer and debates the best detection strategies. This testing is novel as it is the first widespread use of somatic tissue testing to inform genetic analysis and requires the co-ordination of both histopathology and molecular genetics laboratories. However, the clinical use and experience of microsatellite instability (MSI) testing and immunohistochemical analysis have not been reported. A respondent from every cancer genetics centre in the UK (n= 24, response rate 100%) and laboratory performing MSI testing (n= 5, response rate 100%) was interviewed by telephone to ascertain test availability, testing methods, eligibility criteria and post-test management. Twenty centres (83%) offer eligible clients at least one form of tumour testing, and all use tumour testing to determine who should have access to germ line genetic testing. However, no two laboratories used the same testing methods, seven different testing strategies were applied and there was considerable variation in eligibility criteria. The implications of these variations are considered, and recommendations for the development of a consistent service for testing of somatic tissue offered.

The founder mutation MSH2*1906G-->C is an important cause of hereditary nonpolyposis colorectal cancer in the Ashkenazi Jewish population

Hereditary nonpolyposis colorectal cancer (HNPCC) is caused by mutations in the mismatch-repair genes. We report here the identification and characterization of a founder mutation in MSH2 in the Ashkenazi Jewish population. We identified a nucleotide substitution, MSH2*1906G-->C, which results in a substitution of proline for alanine at codon 636 in the MSH2 protein. This allele was identified in 15 unrelated Ashkenazi Jewish families with HNPCC, most of which meet the Amsterdam criteria. Genotype analysis of 18 polymorphic loci within and flanking MSH2 suggested a single origin for the mutation. All colorectal cancers tested showed microsatellite instability and absence of MSH2 protein, by immunohistochemical analysis. In an analysis of a population-based incident series of 686 Ashkenazi Jews from Israel who have colorectal cancer, we identified 3 (0.44%) mutation carriers. Persons with a family history of colorectal or endometrial cancer were more likely to carry the mutation than were those without such a family history (P=.042), and those with colorectal cancer who carried the mutation were, on average, younger than affected individuals who did not carry it (P=.033). The mutation was not detected in either 566 unaffected Ashkenazi Jews from Israel or 1,022 control individuals from New York. In hospital-based series, the 1906C allele was identified in 5/463 Ashkenazi Jews with colorectal cancer, in 2/197 with endometrial cancer, and in 0/83 with ovarian cancer. When families identified by family history and in case series are included, 25 apparently unrelated Ashkenazi Jewish families have been found to harbor this mutation. Although this pathogenic mutation is not frequent in the Ashkenazi Jewish population (accounting for 2%-3% of colorectal cancer in those whose age at diagnosis is <60 years), it is highly penetrant and accounts for approximately one-third of HNPCC in Ashkenazi Jewish families that fulfill the Amsterdam criteria.

Value of predictive genetic testing in management of hereditary non-polyposis colorectal cancer (HNPCC)

OBJECTIVE

To investigate the impact of predictive genetic testing on colonoscopic surveillance in an extended family with hereditary non-polyposis colorectal cancer (HNPCC).

SETTING

Familial Bowel Cancer Service, The Royal Melbourne Hospital, Victoria.

SUBJECTS

96 people registered with the Service who were apparently unaffected members of an extended family that met the classic Amsterdam criteria for HNPCC and carried an MLH1 gene mutation (IVS9 + 3insT).

INTERVENTION

Predictive genetic testing was offered in a cascade manner to at-risk family members; mutation-positive individuals were advised to have annual colonoscopic surveillance, while mutation-negative individuals were withdrawn from surveillance.

MAIN OUTCOME MEASURES

Previous compliance with recommended colonoscopic surveillance; uptake and results of genetic testing; expected effect of genetic test results on number of colonoscopies over five years.

RESULTS

22 of the 96 family members (23%) were not complying with recommended surveillance. Of 48 individuals offered predictive genetic testing, 41 (85%) responded and 39 (81%) underwent testing. Seven of the 39 (18%) were positive for the family-specific mutation, and 32 (82%) were negative. The 39 tested individuals and 37 of their descendants who were registered with the screening program had undergone 70 colonoscopies in the five years before genetic testing. In the five years after testing, only 37 surveillance colonoscopies were planned (annual or two-yearly colonoscopies for the six mutation-positive individuals and five-yearly colonoscopies for four mutation-negative individuals with previously identified adenoma), an almost 50% reduction in colonoscopies.

CONCLUSION

Predictive genetic testing in HNPCC families allows many individuals to be withdrawn from regular colonoscopic surveillance. It may therefore reduce costs, as well as have emotional benefits for many individuals.