Contributions récentes pour l’identification et le dépistage du syndrome de Lynch

Lynch syndrome or hereditary non polyposis colorectal cancer (HNPCC) in a moroccan family: Case report

Introduction and importance

Colorectal cancer is a major global health problem. In 5% of cases, a genetic predisposition to cancer's syndrome is the etiology, such as Lynch syndrome. The population prevalence of Lynch syndrome has been estimated at 1/440. The objectives of this study are to show the interest of the oncogenetic consultation in the management of patients with suspicion of Lynch syndrome.

Case presentation

It is a 70-year-old patient with a family history of different neoplasms. The patient has also been followed for an adenocarcinoma of the colon. An oncogenetic consultation was indicated, which led to the diagnosis of Lynch syndrome, according to the Amsterdam II criteria. A study of the MisMatch Repair genes was requested, to allow a pre-symptomatic diagnosis of apparented subjects at risk, and thus to also allow monitoring and early diagnosis of neoplasms or prophylactic measures.

Discussion

Lynch syndrome is one of the most common cancer susceptibility syndromes. A constitutional deleterious mutation in one of the DNA MisMatch Repair genes, is responsible for nearly 70% of cases of this syndrome. The oncogenetic consultation and the identification of the genetics cause, makes it possible to set up specific monitoring and to offer a pre-symptomatic test to all major relatives of the index case.

Conclusion

This medical observation shows the benefit of the oncogenetic consultation, if a genetic predisposition to cancer's syndrome is suspected. The diagnostic of this predisposition and monitoring of the propositus and his exposed, like in Lynch syndrome will help in the early management of cancers, specially colorectal cancer and endometrial adenocarcinoma.

•

Lynch syndrome in a moroccan family: A case report:

•

It shows the interest of a oncogenetic consultation if we suspect a hereditary predisposition to cancers.

•

And the necessity of the surveillance of the propositus and his exposed relatives, to make possible an early management of cancers.

Role of microsatellite instability in the management of colorectal cancers

Microsatellite instability is the consequence of a deficient mismatch repair system. It has a key role in the diagnostic strategy of Lynch syndrome, where tumours are all characterized by the presence of this phenotype. Microsatellite instability is therefore essential in the selection of colorectal cancer patients in whom a germline analysis of Mismatch Repair genes is possibly indicated. Moreover, microsatellite instability tumours are associated with a good prognosis and a resistance to fluorouracil-based adjuvant chemotherapy, which has a clinical application mainly in stage II colon cancer patients in whom adjuvant chemotherapy has a less beneficial effect than in stage III and outcome in presence of microsatellite instability is excellent. Recent data suggest that impact of microsatellite instability on benefit to fluorouracil-based adjuvant chemotherapy is dependent of the molecular mechanism involved in this genetic instability since an improved survival has been reported with adjuvant fluorouracil in microsatellite instability colorectal cancers of germline origin but not in sporadic cases. Predictive value of microsatellite instability on response to fluorouracil/oxaliplatin adjuvant chemotherapy has been less evaluated but recent studies suggest that the favorable outcome of Microsatellite instability tumours is maintained in patients receiving FOLFOX.

[Hereditary forms of ovarian cancer]

Approximately 5 to 10 % of all ovarian cancers arise in the setting of a major genetic predisposition. The two main hereditary forms of ovarian adenocarcinomas are the hereditary breast/ovarian cancers associated with a BRCA1 or BRCA2 gene mutation and the Lynch syndrome associated with a MLH1, MSH2, MSH6 or PMS2 gene mutation. Their identification and the characterization of a causative germline mutation are crucial and have a major impact for affected women and their relatives in terms of medical management. The aim of this review is to indicate cancer risks associated with these two entities, to evaluate their contribution in the pathogenesis of ovarian cancers and to indicate the clinical data suggestive of these diagnoses, the validated indications for genetic analyses and the current management guidelines. We will also illustrate the diagnostic strategy by reporting a clinical observation.

[HNPCC (hereditary non-polyposis colorectal cancer) or Lynch syndrome: a syndrome related to a failure of DNA repair system]

The HNPCC syndrome (hereditary non polyposis colon cancer) or Lynch syndrome stands for an autosomic dominant condition leading to the most prevalent hereditary colo-rectal cancers (CCR). MMR (mismatch repair)'s genes are involved in carcinogenesis as they play a role in ADNA mismatch repair. Microsatellite instability (MSI+ phenotype) induced by germline mutations is characteristic of such tumors and is necessary to assert the diagnosis. The HNPCC syndrome is associated with a significant increased risk of CCR altogether with endometrium, upper urinary tract and small bowel carcinomas as well as ovarian, biliary system and gastric cancers although of lesser extent. It is of importance to diagnose HNPCC syndrome prior to the treatment starts because it may influence patient's (as well as her/his relatives) disease management (type of surgery, surveillance and screening exams). New French recommendations, developed in 2009, about prophylactic colo-rectal and gynecologic surgeries and monitoring update latest ones published on 2004.

[How and when to search for microsatellite instability in colorectal cancer in 2008?]

Hereditary non polyposis colorectal cancer or Lynch syndrome is due to germline mutation of one the DNA mismatch repair genes. This mutation is associated with an unstable phenotype in tumor DNA characterized by new microsatellite alleles that are absent in matching normal DNA. Besides the Bethesda reference panel, a new panel of 5 mononucleotide microsatellites (BAT25, BAT26, NR21, NR24, NR27) has been proposed, which is more sensitive and faster to use in a multiplex PCR assay. In tumor cells, immunohistochemistry detects the loss of expression of either MLH1, MSH2, MSH6 or PMS2 protein, corresponding to the mutated gene. Immunohistochemistry guides germline analysis, except for MLH1 extinction which may correspond to either MLH1 germline mutation or methylation of MLH1 promoter resulting in inactivation. The latter is mostly due to aging and is often associated to the V600E BRAF gene mutation in tumor DNA. Combination of these 3 somatic analyses should reduce indications of germline mutation analysis in Lynch syndrome.