Immunohistochemical detection of mismatch repair gene proteins as a useful tool for the identification of colorectal carcinoma with the mutator phenotype

Expression of DNA mismatch repair gene hMLH1 and its significance in gastric cancer and premalignant lesions

AIM: To investigate the expression of DNA mismatch repair gene hMLH1 and its clinical significances in gastric cancer and premalignant lesions.

METHODS: Immunohistochemical technique was used to detect the expression of hMLH1 protein in 20 cases of chronic superficial gastritis, 20 cases of chronic atrophic gastritis complicated with intestinal metaplasia, 8 cases of adenomatous polyp, 58 cases of gastric cancer and the corresponding cancer-adjacent mucosa.

RESULTS: The hMLH1 protein was expressed mostly in epithelial cytoplasm and a little in cell nucleus. The positive rate of hMLH1 expression in chronic superficial gastritis and chronic atrophic gastritis with intestinal metaplasia were all 90%, which were significantly higher (χ² = 9.741, P = 0.02) than those in adenomatous polyp (62.5%) and the corresponding cancer-adjacent mucosa (62.1%). The positive rate of hMLH1 expression was not significantly different between gastric cancer (72.4%) and the others (P > 0.05). Of 58 cases of cancer-adjacent mucosa, 21 (36.2%) were with chronic superficial gastritis, and 37 (63.8%) with chronic atrophic gastritis and intestinal metaplasia. The positive rates of hMLH1 expression were similar between the 21 and 37 cases, but they were both markedly lower than those in the nonneoplastic mucosa (χ² = 9.885, P = 0.02).

CONCLUSION: Absence of hMLH1 expression may be one of the early molecular events in the carcinogenesis of gastric cancer. Timely visiting and monitoring chronic gastric patients with absence of hMLH1 protein expression may help to achieve early diagnosis of gastric cancer.

Clinicopathological and molecular genetic analysis of HNPCC in China

AIM: To explore the clinicopathological and molecular genetic features of hereditary nonpolyposis colorectal cancer (HNPCC) in Chinese population.

METHODS: We collected 16 Chinese HNPCC families from Wenzhou, Zhejiang Province, China. Tumor tissues and peripheral white blood cells were studied using microdissection, microsatellite analysis, immunostaining of hMSH2 and hMLH1 proteins and direct DNA sequencing of hMSH2 and hMLH1 genes.

RESULTS: (1) A total of 50 patients had CRC. Average age at diagnosis of the first CRC was 45.7 years; 40.9% and 28.7% of the CRCs were located proximal to the splenic flexure and in the rectum, respectively. Thirty-eight percent of the colorectal cancer patients had synchronous and metachronous CRC. 34.4% and 25% of the CRCs were poor differentiation cancer and mucinous adenocarcinoma, respectively. Fourteen extracoloni tumors were found, and the hepatic cancer was the most common tumor type. Twenty-one patients whose median survival time was 5.7 years died during 1-23 years. Twenty-nine patients have survived for 1-28 years, 58.6%, 41.4% and 24.1% patients have survived for more than 5, 10 and 15 years, respectively; (2) All nine tumor-tissues showed microsatellite instability (MSI) at more than two loci. Four tumor-tissues lost hMSH2 protein expression and one lost hMLH1 protein expression. Three pathological germline mutations were identified from five genetically analyzed families; two of three mutations had not been reported previously as they were a transition from C to A in exon 14 (codon 743) of hMSH2 and a TTC deletion in exon 14 (codon 530) of hMLH1.

CONCLUSION: Chinese HNPCC have specific clinicopathological features, such as early onset, propensity to involve the proximal colon, and high frequency of multiple CRCs, liver cancer more frequent than endometrial cancer. Chinese HNPCC showed relatively frequent germline mutation of mismatch repair (MMR) genes that correlated closely with high-level MSI and loss of expression of MMR genes protein.

Clinicopathological and molecular genetic analysis of 4 typical Chinese HNPCC families

AIM: To study the clinicopathological and mole cular genetic characteristics of typical Chinese hereditary nonpolyposis cotorectal cancer (HNPCC) families.

METHODS: Four typical Chinese HNPCC families were analyzed using microdissection, microsatellite instability analysis, immunostaining of hMSH2 and hMLH1 proteins and direct DNA sequencing of hMSH2 and hMLH1 genes.

RESULTS: All five tumor tissues of 4 probands from the 4 typical Chinese HNPCC families showed microsatellite instability at more than two loci (MSI-H or RER+ phenotype). Three out of the 4 cases lost hMSH2 protein expression and the other case showed no hMLH1 protein expression. Three pathological germline mutations (2 in hMSH2 and 1 in hMLH1), which had not been reported previously, were identified. The same mutations were also found in other affected members of two HNPCC families, respectively.

CONCLUSION: Typical Chinese HNPCC families showed relatively frequent germline mutation of mismatch repair genes. High-level microsatellite instability and loss of expression of mismatch repair genes correlated closely with germline mutation of mismatch repair genes. Microsatellite instability analysis and immunostaining of mismatch repair gene might serve as effective screening methods before direct DNA sequencing. It is necessary to establish clinical criteria and molecular diagnostic strategies more suitable for Chinese HNPCC families.