Familial and genetic aspects of colorectal carcinogenesis

Detection of aberrations of ubiquitin-conjugating enzyme E2C gene (UBE2C) in advanced colon cancer with liver metastases by DNA microarray and two-color FISH

Using DNA microarrays, the expression profiles of 1,700 genes in the primary tumor, liver metastases and paired normal tissue obtained from nine patients with advanced colorectal cancer was studied. Twenty genes were upregulated and only one gene was downregulated in the primary tumors. In the liver metastases, 39 genes were upregulated and only three genes were downregulated. There was no significant difference in gene expression between the primary tumors and the liver metastases. The most highly overexpressed gene in both the primary tumors and the liver metastases was the ubiquitin-conjugating enzyme E2C gene (UBE2C), located at 20q13.1. Additionally, two-color FISH analysis using probes for the region 20q13.1 and the chromosome 20 centromere revealed that amplification at 20q13.1 had occurred in 5 of 10 (50%) colon cancers. Comparison between the levels of gene expression and FISH results revealed that UBE2C expression is significantly changed by amplification at 20q13.1, suggesting genomic amplification as one mechanism of increased UBE2C expression. Our results showing aberrations in levels of gene expression and locus copy number of UBE2C suggest that this gene may play an important role in tumor progression leading to advanced colon cancer with liver metastasis.

Family history of cancer and risk of colorectal cancer in Italy

Subjects with a family history of colorectal cancer (CRC) are at increased risk of CRC, but quantification of the risk in different populations, the possible differences in risk according to localization of the cancer and the association of family history of other cancers with CRC risk are still open issues. We have therefore analysed data from a multicentric case-control study conducted in six Italian areas between 1992 and 1996 of 1225 incident cases of colon cancer, 728 cases of rectal cancer and 4154 controls admitted for acute conditions to the same network of hospitals as the cases. Unconditional logistic regression models including terms for gender, age, study centre, years of education and number of siblings were used to estimate the odds ratios (ORs) of CRC according to various aspects of history of CRC and other cancers in first-degree relatives. The OR for family history of CRC was 3.2 (95% confidence interval, CI, 2.5-4.1) for colon cancer and 2.2 (95% CI 1.6-3.1) for rectal cancer. Colon cancer was significantly associated with a family history of stomach (OR 1.4), bone (OR 2.1) and kidney (OR 2.3) cancers, while rectal cancer was significantly associated with a family history of lymphomas (OR 2.8). There was a 30% higher risk of colon and rectal cancer in subjects with a family history of any cancer, excluding intestine. The ORs for family history of CRC were 5.2 for colon and 6.3 for rectum when the proband's age was below 45 years. The ORs were similar when the affected relative was a parent or a sibling and in different strata of age of relative(s). For subjects with two or more first-degree relatives with CRC, the risk was 6.9 for the right colon, 5.8 for the transverse and descending colon, 3.8 for the sigma, 3.2 for the rectosigmoid junction and 1.9 for the rectum. This study confirms that a family history of CRC in first-degree relatives increases the risk of both colon and rectal cancer, the association being stronger at younger ages and for right colon.

Topographic genotyping of colorectal carcinoma: from a molecular carcinogenesis model to clinical relevance

BACKGROUND

In recent years, as a result of refinement in molecular biology techniques, significant progress has been made in the understanding of colorectal carcinogenesis. Particular attention has been drawn to identification of genetic mutation that may predispose to colorectal carcinoma (familial syndromes) and may affect tumor behavior and prognosis (sporadic cases).

CONCLUSIONS

Our method of topographic genotyping of human colonic carcinomas has shown a correlation between K-ras-2 and p53 mutations and stage at diagnosis as well as long-term survival. Data from other investigators in this field confirm the importance of genetic analysis of human colorectal tumors. These findings are likely to impact management by allowing a more individualized therapeutic approach.

Microsatellite instability: new aspects in the carcinogenesis of colorectal carcinoma

Very recently a new molecular mechanism in the tumorigenesis of colorectal carcinoma has been described which is closely linked to hereditary non-polyposis colonic cancer (HNPCC). Ubiquitous changes in the length of simple repetitive DNA sequences between constitutional and tumour DNA occur in about 90% of cases of HNPCC and in about 15% of cases of non-familial, sporadic colorectal carcinoma. Such microsatellite instabilities have been shown to be the phenotypical marker of mutations in the human homologues of prokaryotic mismatch repair genes (MutS, MutL, MutH). These data provide crucial new tools in the detection of patients at high risk of developing colon cancer and other HNPCC-related carcinomas. In addition, these developments provide new insights into a new, presumably primary event in oncogenesis, i.e. the occurrence of mutations in genomic stability genes leading to an increased cellular mutation rate ("mutator phenotype") and thus to cancer.