Using genetic information to make surgical decisions: report of a case of a 13-year-old boy with colon cancer

Genetic predisposition to colorectal cancer: new pieces in the pediatric puzzle

Colorectal cancer is rare in childhood. The 2 best characterized familial syndromes, hereditary nonpolyposis colorectal cancer (HNPCC, Lynch syndrome) and familial adenomatous polyposis (FAP), are autosomal dominant inherited disorders. HNPCC is relevant to pediatric gastroenterology practice because children and adolescents with underlying colorectal cancer can have germ-line mutations of mismatch repair genes. Recent attention has focused on characterizing genetic predisposition to attenuated FAP in individuals who do not have germ-line mutations in the APC gene. The identification of a second mechanistic explanation called MYH-associated polyposis (MAP), which is an autosomal-recessive condition, has important implications for both screening and management strategies. Hereditary colorectal cancer including HNPCC, FAP, attenuated FAP and MYH-associated polyposis in children are the subject of this review.

Germline characterization of early-aged onset of hereditary non-polyposis colorectal cancer

OBJECTIVES

Hereditary non-polyposis colorectal cancer (HNPCC) is characterized by the early onset of colorectal cancer (approximately 40 years). Adolescent colorectal cancer is unusual in HNPCC families. We speculated that some DNA mismatch repair germline mutations might be associated with early onset of disease.

STUDY DESIGN

Genomic DNA was extracted from members of a kindred with virulent HNPCC fitting the Amsterdam Criteria for HNPCC and sequenced for 2 DNA mismatch repair genes, hMSH2 and hMLH1. A sigmoid adenocarcinoma from the 14-year-old proband was analyzed for highfrequency microsatellite instability and immunostained for DNA mismatch repair gene expression.

RESULTS

A germline mutation was identified at nucleotide 676 (codon 226) of the hMLH1 gene. The C to T transition created a nonsense mutation, truncating the hMLH1 protein. This mutation also alters the splice donor sequence, because nucleotide 676 is 2 base pairs from the 3' end of the exon 8. The proband's tumor demonstrated high-frequency microsatellite instability and displayed loss of hMLH1 expression, indicating bi-allelic inactivation of hMLH1.

CONCLUSIONS

A complex mutation of hMLH1 at codon 226 is associated with adolescent onset of colorectal cancer in an HNPCC family. Genetic screening of other suspected HNPCC families with unusually young members with cancer might reveal certain genotypes with particularly virulent forms of this disease.

Evaluation of colonoscopic sized biopsies for microsatellite instability and adenomatous polyposis coli (APC) variants

OBJECTIVE

Knowledge of certain genetic changes associated with the development of colorectal cancer may influence surgical treatment in the future. Cancers are known to show intratumoural genetic heterogeneity. The aim of this study was to determine whether colonoscopic sized biopsies provide enough tissue to overcome the effects of tumour heterogeneity for the results of genetic analysis to be representative of the tumour as a whole.

PATIENTS AND METHODS

Using colonoscopic biopsy forceps, samples were taken from 30 resected colorectal cancers and investigated for microsatellite instability (MSI) at five loci and changes in the adenomatous polyposis coli gene (APC) by single-stranded conformational polymorphism analysis. Identical genetic analysis was carried out on larger specimens taken from each of these cancers to determine whether the molecular findings from the large specimen were the same as those from colonoscopic sized biopsies.

RESULTS

The microsatellite instability and APC status of the colonoscopic sized biopsies and those from larger specimens were completely consistent.

CONCLUSION

These results suggest that colonoscopic sized biopsies are reliable in determining the MSI status and APC variants of individual colorectal cancers.