Missense polymorphisms in the adenomatous polyposis coli gene and colorectal cancer risk.

PURPOSE: Whereas truncating germline mutations of the adenomatous polyposis coli (APC) gene give rise to familial adenomatous polyposis, missense polymorphisms of APC may confer a weaker risk for colorectal cancer. METHODS: We sequenced the entire open reading frame of the APC gene and tested for two common MYH mutations in a population-based series of patients with colorectal cancer and 5 to 99 adenomas. Missense adenomatous polyposis coli alterations identified in this colorectal cancer multiple-polyp population were analyzed in a population-based series of patients with colorectal cancer and healthy control subjects. RESULTS: Germline APC or mutY human homologue (MYH) alterations were identified in 16 of 39 colorectal cancer-multiple polyp patients. Four missense APC gene alterations (S130G, E1317Q, D1822V, G2502S) were observed in 13 individuals and 3 additional patients carried presumed pathogenic (APC Y94X, biallelic MYH Y165C and heterozygous MYH G382D) mutations. When independently assessed in 971 patients with colorectal cancer and 954 healthy control subjects, none of the identified missense APC alterations conferred a significantly increased risk for colorectal cancer, odds ratio (95 percent confidence intervals): S130G = 3.1 (0.29-32.25), E1317Q = 1.08 (0.59-2.74), G2502S = 1 (0.65-1.63), D1822V (heterozygous) = 0.79 (0.64-0.98), D1822V (homozygous) = 0.82 (0.63-1.27). CONCLUSIONS: Germline missense APC alterations observed in 33 percent of patients with multiple colorectal neoplasms seemed to play a limited role in colorectal cancer risk when independently assessed by a population-based, case-control analysis.

Risk of colorectal cancer in monoallelic and biallelic carriers of MYH mutations: a population-based case-family study.

Previous case-control studies have suggested that carriers of monoallelic germline mutations in the MYH gene may be at increased risk of colorectal cancer. We applied a kin-cohort design, using a modified segregation analysis, to estimate the colorectal cancer risk using 300 first-degree relatives of 39 colorectal cancer cases who were monoallelic or biallelic carriers of MYH mutations. We found that monoallelic carriers had a 3-fold increased risk of colorectal cancer (hazard ratio, 2.9; 95% confidence interval, 1.2-7.0; P = 0.02) and biallelic carriers a 50-fold increased risk (hazard ratio, 53; 95% confidence interval, 14-200; P < 0.0001). This analysis illustrates the potential of family analysis to estimate cancer risk for low-frequency mutations and, based on the proportion of relatives predicted to be carriers, we believe that this constitutes the largest study of monoallelic carriers to date.

High frequency of hereditary colorectal cancer in Newfoundland likely involves novel susceptibility genes.

PURPOSE: Newfoundland has one of the highest rates of colorectal cancer in North America. The most common hereditary form of colorectal cancer is hereditary nonpolyposis colorectal cancer caused by mutations in genes involved in mismatch repair. Our purpose was to determine the proportion of hereditary colorectal cancer and to determine the genetic basis of disease in both population and clinically referred cohorts from Newfoundland. EXPERIMENTAL DESIGN: Seventy-eight colorectal cancer patients were accrued over a 2-year period from the Avalon Peninsula of Newfoundland. We also examined 31 hereditary nonpolyposis colorectal cancer-like families, which had been referred to the Provincial Medical Genetics Program. Tumors from probands were tested by immunohistochemistry for deficiencies in MLH1, MSH2, and MSH6 proteins and tested for DNA microsatellite instability. Mutation analyses of MLH1, MSH2, and MSH6 were undertaken by direct sequencing and an assay to detect deletions, amplifications, and rearrangements in MSH2 and MLH1. RESULTS: We identified eight population-based families that fulfill the Amsterdam I or II criteria, 4 (50%) of which seem to have hereditary cancer not attributable to the most commonly mutated mismatch repair genes. In addition, in 16 of 21 (76%) referred families fulfilling Amsterdam I or II criteria, no mutations were found in the three most commonly altered mismatch repair genes, and tumor analyses corroborated these findings. CONCLUSIONS: It seems that strong and novel genetic causes of hereditary colorectal cancer are responsible for a high proportion of colorectal cancer in this population. Conditions are suitable for the identification of these genes by linkage studies of large Newfoundland cancer families.

Germline MYH mutations in a clinic-based series of Canadian multiple colorectal adenoma patients.

OBJECTIVES: MYH is a member of the DNA base excision repair (BER) pathway and mutations of this gene predispose to the development of colorectal neoplasia in an autosomal recessive transmission pattern. Our objective was to determine the significance of MYH mutations in a series of Canadian patients with multiple adenomas. METHODS: We screened for germline MYH mutations (by dHPLCO) in 20 clinic-based multiple adenoma patients who were adenomatous polyposis coli (APC) mutation-negative. Suspected mutations were confirmed by sequence analysis. RESULTS: Six of 20 (30%) patients carried pathogenic biallelic MYH mutations, 1 Y165C homozygote and 5 compound heterozygotes of other sequence variants. We identified three novel variants, Q377X, 1314delA, and P281L, which are likely pathogenic. Twenty-nine relatives of the Y90X/1103delC compound heterozygous carrier were also screened for germline MYH mutations, and 1 homozygous and 14 heterozygous carriers were identified. CONCLUSIONS: Among patients with multiple adenomas, biallelic MYH mutations account for approximately 30% of APC mutation negative cases and two thirds of these carry mutations other than the "common" Y165C and G382D variants. Clinical screening algorithms which focus only on the Y165C and G382D alleles are inadequate since additional pathogenic mutations may be identified by screening the entire gene.

A multicenter phase II study of "adjuvant" irinotecan following resection of colorectal hepatic metastases.

OBJECTIVES: This study evaluates the efficacy and toxicity of single-agent irinotecan following hepatectomy for metachronous colorectal metastases, and examines the predictive value of p27 and p53 expression and of microsatellite instability (MSI) status. METHODS: Twenty-nine patients, previously treated with 5-fluorouracil, with operable hepatic colorectal metastases underwent hepatectomy and received adjuvant irinotecan (thrice weekly) for 6 planned cycles. Metastases were examined for p53 and p27 expression by immunohistochemistry and for MSI using mono- and dinucleotide markers. RESULTS: The starting dose of irinotecan was 350 mg/m2 (in 3 patients), 300 mg/m2 (n = 14), and 250 mg/m2 (n = 12). Four patients failed to complete 6 cycles (2 progressive disease and 2 toxicity). Grade > or =3 toxicity was experienced in 8% of cycles (13 of 165). The estimated median relapse-free survival (RFS) was 45.2 months. RFS at 18 months was estimated to be 59% (95% confidence interval [CI], 43-80), 2-year overall survival (OS) was 85% (95% CI, 72-99.8), and the median follow-up was 27.9 months. Six patients (21%) have died; median OS has not been reached. In univariate analyses, p27 and MSI status were not predictive for RFS while p53 approached statistical significance (P = 0.051). Duration of chemotherapy was the only significant predictive factor (P = 0.006). CONCLUSION: The tolerability of this regimen after major liver resection supports further evaluation of irinotecan-based adjuvant chemotherapy in this group of patients.

Association between biallelic and monoallelic germline MYH gene mutations and colorectal cancer risk.

The MutY human homologue (MYH) gene encodes a member of the base excision repair pathway that is involved in repairing oxidative damage to DNA. Two germline MYH gene mutations that result in Myh proteins containing amino acid substitutions Y165C and G382D (hereafter called the Y165C and G382D mutations) are associated with adenomatous poly-posis and colorectal cancer among patients from several European poly-posis registries. We used a population-based series of 1238 colorectal cancer patients and 1255 healthy control subjects from Ontario, Canada, to examine the risk of colorectal cancer among biallelic and monoallelic germline MYH Y165C and G382D mutation carriers. The entire MYH gene coding region was screened in all MYH Y165C and G382D mutation carriers. Compared with noncarriers, biallelic and monoallelic germline MYH gene mutation carriers had an increased risk of colorectal cancer and were more likely to have first-or second-degree relatives with colorectal cancer (relative risk = 1.54, 95% confidence interval = 1.10 to 2.16). The increased risk of colorectal cancer in biallelic and monoallelic MYH gene mutation carriers was not consistently associated with the development of multiple adenomatous polyps. Loss of heterozygosity in at least one of four loci in MYH was detected in eight (47%) of 17 colorectal tumors from monoallelic MYH gene mutation carriers but in only two (20%) of 10 colorectal tumors from biallelic MYH gene mutation carriers. These two MYH gene mutations may account for a substantial fraction of hereditary colorectal cancer.

Microsatellite instability as a prognostic factor in resected colorectal cancer liver metastases.

BACKGROUND: Two distinct genetic mutational pathways characterized by either chromosomal instability or high-frequency microsatellite instability (MSI-H) are currently recognized in the pathogenesis of colorectal cancer (CRC). Recently, it has been shown that patients with primary CRC that displays MSI-H have a significant, stage-independent, multivariate survival advantage. Untreated CRC hepatic metastases are incurable and are associated with a median survival of 4 to 12 months. Conversely, surgical resection in selected patients results in a 20% to 50% cure rate. The aim of this study was to investigate the prognostic importance of MSI-H in patients undergoing resection of hepatic CRC metastases. METHODS: DNA was extracted from paraffin-embedded, resected metastatic CRC liver lesions and corresponding normal liver parenchyma from 190 patients. MSI-H status was determined by polymerase chain reaction-based evaluation of the noncoding mononucleotide repeats BAT-25 and BAT-26. RESULTS: MSI was detected in tumors from 5 (2.7%) of the 190 CRC patients. All MSI-H tumors were in patients with node-positive CRC primary tumors. The median survival after hepatic resection of MSI-H and non-MSI-H tumors was 67 and 61 months, respectively (P = .9). CONCLUSIONS: These data suggest that MSI-H is not a common feature in resected CRC liver metastases and do not suggest a role for MSI in stratifying good versus poor prognosis in these patients.

Gastrointestinal cancers and neurofibromatosis type 1 features in children with a germline homozygous MLH1 mutation.

Heterozygous germline DNA mismatch repair gene mutations are typically associated with hereditary nonpolyposis colorectal cancer. The molecular hallmark of this syndrome is high-frequency microsatellite instability in the tumors. Rare childhood cases with homozygous or compound heterozygous DNA mismatch repair gene mutations have a described predisposition to leukemia, lymphoma, and brain tumors but not to gastrointestinal cancer. We have now characterized a family in which 2 children with a homozygous germline DNA mismatch repair gene mutation developed early-onset gastrointestinal cancers. The 11-year-old proband had café-au-lait macules and developed metastatic duodenal adenocarcinoma that arose in a tubulovillous adenoma. His 9-year-old sister with café-au-lait macules and axillary freckling presented with malignant colon polyps. A 6-year-old sister with café-au-lait macules, hairy nevi, and a plexiform neurofibroma of the tongue has no malignancies to date. The family history did not fulfill the Amsterdam criteria for hereditary nonpolyposis colorectal cancer, but 2 relatives in their 60s had gastric cancer and colorectal cancer, whereas the parents, who are first cousins, remain cancer free. The proband's metastatic duodenal cancer and his sister's malignant colon polyps had high-frequency microsatellite instability but had detectable MLH1, MSH2, and MSH6 proteins by immunohistochemistry. Because some germline DNA mismatch repair gene deficiencies are associated with apparently intact immunohistochemical DNA mismatch repair gene expression in tumors, we proceeded to DNA sequencing, which showed that all 3 children had a germline homozygous MLH1 missense mutation (exon 18, codon 687, CGG-->TGG), whereas both parents were heterozygous for this mutation.