Germline, somatic and epigenetic events underlying mismatch repair deficiency in colorectal and HNPCC-related cancers.

High-frequency microsatellite instability (MSI-H) results from deficiency in nucleotide mismatch repair. It contributes significantly to carcinogenesis in the human colorectal mucosa. Here we study 41 colorectal and three other HNPCC-related cancers with MSI-H to provide comprehensive information on the mechanisms of inactivation of the two major proteins involved, hMLH1 and hMSH2. Seventeen of the patients had family histories meeting the criteria for Bethesda grades 1, 2 or 3. Of these familial cases, 14 (83%) had early-onset disease, defined on the basis of diagnosis prior to the age of 50, but in three the disease was of late onset (>50 years). A second subset of 20 patients had early onset disease without family history. The remaining seven patients were selected to allow comparisons with sporadic, late-onset disease, the molecular basis of which has been extensively reported elsewhere. We stratified the tumours initially on the basis of hMLH1 or hMSH2 protein deficiency, detected by immunohistochemistry, and then by analysis of germline and somatic mutation, mRNA transcription, loss of heterozygosity (LOH) at the hMLH1 and hMSH2 loci, and methylation status in two regions of the hMLH1 promoter. The functional significance of several of these changes in the MSI-H tumours was confirmed by comparisons with 16 tumours with low-frequency microsatellite instability and 56 tumours with stable microsatellites. As anticipated, patients with family histories usually showed germline mutation of hMSH2 or hMLH1. In many cases the residual normal allele was silenced in their tumours by loss of heterozygosity (LOH). The small subset of late-onset, sporadic cases confirmed the preponderance in this group of biallelic hMLH1 promoter methylation. In the early-onset, apparently sporadic subset there were 11 tumours with hMLH1 deficiency, five with hMSH2 deficiency and four with no detectable abnormality in expression of either protein. These showed a complex mixture of lesions, including germline and somatic mutations, promoter methylation, LOH, suppression of wild-type RNA by as yet undiscovered mechanisms, or no detectable abnormality in any of these parameters. Evidence is presented to indicate that methylation in proximal region of the hMLH1 promoter is a more reliable correlate of transcriptional silencing in colorectal cancers than methylation in upstream region. These observations have significant implications for management of patients with MSI-H tumours.

Quantification of plasma beta-catenin mRNA in colorectal cancer and adenoma patients.

PURPOSE: Colorectal cancer is an important cause of cancer deaths. Here, we focused our investigation on the beta-catenin gene which is implicated in colorectal carcinogenesis and tested whether beta-catenin mRNA is detectable in the plasma of colorectal carcinoma and adenoma patients using quantitative reverse transcriptase-PCR. EXPERIMENTAL DESIGN: Plasma beta-catenin mRNA was measured from 58 colorectal carcinoma patients, 49 colorectal adenoma patients, and 43 apparently normal subjects using intron-spanning primers and Taqman probes. Five clinicopathological parameters were studied and correlated with plasma beta-catenin mRNA concentration. Additionally, 19 colorectal carcinoma patients after tumor removal were also recruited for plasma beta-catenin mRNA measurement to further demonstrate the clinical usefulness of this test. RESULTS: beta-catenin mRNA was detected with median concentrations of 8737 (range: 1480-933100), 1218 (range: 541-2254) and 291 (range: 0-1366) copies/ml plasma in colorectal carcinoma, colorectal adenoma, and apparently normal subjects, respectively. Statistical analysis demonstrated that plasma beta-catenin mRNA concentration was correlated to tumor stage but not sex, age, lymph node status, and degree in differentiation. Moreover, plasma beta-catenin mRNA concentration decreased significantly after tumor removal in 16 of 19 (84%) colorectal carcinoma patients. CONCLUSIONS: We conclude that plasma beta-catenin mRNA may potentially serve as a marker for colorectal cancer.

Smoking, drinking and colorectal cancer in Hong Kong Chinese: a case-control study.

Expert opinions differ on the causal role of cigarettes and alcohol in colorectal cancer. This study investigates such associations in Hong Kong Chinese. A hospital-based case-control study was conducted from April 1998 to March 2000. Newly diagnosed colorectal adenocarcinoma and sex- and age-matched inpatient controls without gastrointestinal and malignant conditions were included. Structured interviews were conducted using a validated questionnaire to study any association of smoking, drinking and the lifelong extent of such exposures with colorectal cancer risk. We successfully interviewed 822 cases and 926 controls. Current regular cigarette smokers had an increased rectal cancer risk (adjusted OR = 1.44; 95% CI = 1.001-2.06). Increasing tertiles of smoking duration in ever smokers was also associated with increased rectal cancer risk (p trend = 0.038). An increased risk of colorectal cancer was found in current drinkers (adjusted OR = 1.42; 95% CI = 1.09-1.85) and in those who drank > or = 4 days (current and ex-drinkers) or > 4 units (ever and ex-drinkers) weekly. Moreover, colorectal cancer risk was found to decrease with increasing duration of drinking abstention (p trend = 0.006). This is the first report of a positive association between cigarette smoking and rectal cancer risk in a Chinese population. Current drinkers and those who drank regularly and heavily had increased colorectal cancer risk. Moreover, this study is the first to show that drinking cessation could be effective in reversing such increased risk in a duration-dependent manner. These new findings are important for cancer prevention and healthcare promotion.

MSH2 c.1452-1455delAATG is a founder mutation and an important cause of hereditary nonpolyposis colorectal cancer in the southern Chinese population.

Hereditary nonpolyposis colorectal cancer (HNPCC) accounts for approximately 2% of all colorectal cancer (CRC) cases and is the most common hereditary CRC syndrome. We have previously reported a high incidence of microsatellite instability (MSI) and germline mismatch repair (MMR) gene mutations in young Hong Kong Chinese with CRC. Ongoing studies at the Hereditary Gastrointestinal Cancer Registry in Hong Kong have revealed a unique germline MSH2 c.1452-1455delAATG mutation that has not been reported in other ethnic groups. Detailed analysis showed that this specific MSH2 mutation constituted 21% of all germline MMR gene mutations and 36% of all MSH2 germline mutations identified. We designed a specific PCR-based diagnostic test on paraffin-embedded tissues and identified this germline mutation in 2 (1.5%) of 138 consecutive patients with early-onset CRC (<46 years of age at diagnosis). Haplotype analysis was performed using 11 microsatellite markers located between D2S391 and D2S123. All 10 families had the same disease haplotype, suggesting a founder effect. These 10 families all originated from the Chinese province of Guangdong, which historically included Hong Kong. It is the most populous of the Chinese provinces, with a population of >93 million. Further analysis suggested that this founder mutation may date back to between 22 and 103 generations ago. The identification of this MSH2 founder mutation has important implications for the design of mutation-detection strategies for the southern Chinese population. Since there were major emigrations from Hong Kong and Guangdong province during the 19th and 20th centuries, this finding is also significant for Chinese communities worldwide.