Les cancers colorectaux héréditaires vus par le pathologiste

The pathologist's role in the management of hereditary colorectal cancer is important. The pathologist may suspect a familial cancer when particular morphological and/or clinical criteria are present or give a response to a clinical request in the context of a possible hereditary cancer. In this setting, the pathologist's conclusions have necessarily to be integrated to a precise environment, and if needed, followed by an oncogenetic consultation and a germline mutation research. The aim of this article is to present the main aspects of hereditary colon cancers that a pathologist may see, but also to highlight the histopathological characteristics and the place of the pathologist in the management of these different entities.

c.1227_1228dupGG (p.Glu410Glyfs), a frequent variant in Tunisian patients with MUTYH associated polyposis

INTRODUCTION

Familial adenomatous polyposis (FAP) is an autosomal dominant-inherited disease caused by germline variants in the APC gene. It is characterized by the development of hundreds to thousands of adenomatous polyps in colon and rectum. Recently, biallelic germline variants in the base excision repair (BER) gene: MUTYH have been identified in patients with attenuated FAP and/or negative APC result. It can be responsible for an autosomal recessive inherited colorectal cancer syndrome (MAP syndrome: MUTYH-associated polyposis).

OBJECTIVE

The aim of this study was to evaluate germline variants of MUTYH gene in Tunisian patients with attenuated FAP.

METHODS

thirteen unrelated patients from Tunisia with attenuated FAP were screened for MUTYH germline variants. Direct sequencing was performed to identify point variants in this gene.

RESULTS

A Biallelic MUTYH germline variant were found in all patients and showed an attenuated polyposis phenotype almost of them without extra-colic manifestations: The known pathogenic frameshift variant c.1227_1228dupGG (p. Glu410Glyfs) was found, in homozygous state, in 13 index patients.

CONCLUSION

Patients with attenuated familial adenomatous polyposis (<=100) and no obvious vertical transmission of the disease should be considered for MUTYH gene testing.

Serrated polyposis: colonic phenotype, extracolonic features, and familial risk in a large cohort

BACKGROUND

Serrated polyposis is a poorly understood and likely underdiagnosed condition. Little is known regarding the colorectal cancer risk, extracolonic phenotype, and cause of serrated polyposis.

OBJECTIVE

The aim of this study is to describe the clinical and family history features of a large cohort of individuals with serrated polyposis.

DESIGN

This is a retrospective cohort study from 2 prospectively collected registries.

PATIENTS

Patients meeting the updated 2010 World Health Organization criteria for serrated polyposis were included.

MAIN OUTCOME MEASURES

We report descriptive statistics for clinical and family history factors.

RESULTS

A total of 52 individuals met criteria for serrated polyposis. Of these, one had Lynch syndrome and was not included in the statistical analyses. Median age at serrated polyposis diagnosis was 51 years (range, 18-77). Twenty-four (47%) patients were male, and 25 (49%) had a history of smoking. Two hundred sixty-eight lower endoscopic procedures were performed; 42 (82%) patients had colorectal adenomas, 8 (16%) had a personal history of colorectal cancer (only 1 was diagnosed during follow-up), 12 (24%) had extracolonic tumors (4 had more than 1 primary tumor), and 19 (37%) reported a family history of colorectal cancer. Esophagogastroduodenoscopy in 30 individuals revealed only 1 (3%) with unexplained gastroduodenal polyps. No association was found between colorectal cancer diagnosis and sex, age at serrated polyposis diagnosis, extracolonic tumor, history of adenoma, or smoking status.

LIMITATIONS

This was a retrospective study with no comparison groups.

CONCLUSIONS

Gastroduodenal polyps are uncommon and likely not associated with serrated polyposis. Although extracolonic tumors were common in our cohort, it is still unclear whether these are associated with serrated polyposis. Our data, along with previous studies, support an association between serrated polyposis and smoking. Further work is still needed to clarify the effect of smoking on polyp development/progression in serrated polyposis.

Oxidative DNA damage drives carcinogenesis in MUTYH-associated-polyposis by specific mutations of mitochondrial and MAPK genes

MUTYH is a DNA-base-excision-repair gene implicated in the activation of nuclear and mitochondrial cell-death pathways. MUTYH germline mutations cause an inherited polyposis, MUTYH-associated-polyposis, characterized by multiple adenomas and increased susceptibility to colorectal cancer. Since this carcinogenesis remains partially unknown, we searched for nuclear and mitochondrial gene alterations that may drive the tumorigenic process. Ninety-six adenomas and 7 carcinomas from 12 MUTYH-associated-polyposis and 13 classical/attenuated adenomatous polyposis patients were investigated by sequencing and pyrosequencing for the presence of mutations in KRAS, BRAF, MT-CO1/MT-CO2 and MT-TD genes. KRAS mutations were identified in 24% MUTYH-associated-polyposis vs 15% classical/attenuated familial polyposis adenomas; mutated MUTYH-associated-polyposis adenomas exhibited only c.34G>T transversions in codon 12, an alteration typically associated with oxidative DNA damage, or mutations in codon 13; neither of these mutations was found in classical/attenuated familial polyposis adenomas (P<0.001). Mutated MUTYH-associated-polyposis carcinomas showed KRAS c.34G>T transversions, prevalently occurring with BRAFV600E; none of the classical/attenuated familial polyposis carcinomas displayed these alterations. Comparing mitochondrial DNA from lymphocytes and adenomas of the same individuals, we detected variants in 82% MUTYH-associated-polyposis vs 38% classical/attenuated familial polyposis patients (P=0.040). MT-CO1/MT-CO2 missense mutations, which cause aminoacid changes, were only found in MUTYH-associated-polyposis lesions and were significantly associated with KRAS mutations (P=0.0085). We provide evidence that MUTYH-associated-polyposis carcinogenesis is characterized by the occurrence of specific mutations in both KRAS and phylogenetically conserved genes of mitochondrial DNA which are involved in controlling oxidative phosphorylation; this implies the existence of a colorectal tumorigenesis in which changes in mitochondrial functions cooperate with RAS-induced malignant transformation.

Genetic testing by cancer site: colon (polyposis syndromes)

Hereditary colonic polyposis conditions are all characterized by high rates of cancer, but they have diverse phenotypes, genetic heterogeneity, and assorted inheritance patterns. The most well known of these conditions include familial adenomatous polyposis, attenuated familial adenomatous polyposis, MUTYH (MutY human homolog)-associated polyposis, Peutz-Jeghers syndrome, juvenile polyposis syndrome, and Cowden syndrome. Early recognition of these conditions is not only vital for management in affected individuals, but also for prevention and early detection in at-risk relatives. Reviewed here are the genetic testing strategies for colonic polyposis, as well as an overview of characteristic features and management considerations for these syndromes.