Colon Cancer

Introduction:

Over 130,000 cases of colorectal cancer are diagnosed annually, and over 50,000 deaths. Colorectal cancer is the second most common cause of all cancer deaths. Colon and rectum cancers together called colorectal cancer afflict the lining of the large intestine. All forms of colon cancer arise from colorectal polyps that line the large intestine.

While there are environmental risk factors for cancer such as smoking, diet, and exposure to carcinogens, colon cancer is one of the most common inherited cancers. Hundreds of genes are involved in controlling cell division and ensuring DNA replication functions properly. Important genes found to be involved in colorectal cancer include MSH2 and MSH6 on chromosome 2 and MLH1 on chromosome 3. The protein products of these genes help repair DNA replication errors while functioning properly. If these genes are mutated they will code for faultly protein products that do not properly repair DNA replication errors. This can lead to irregular cell grown and in this case, colon cancer.

Symptoms:

While most cases of colon cancer do not have symptoms, common symptoms of colon cancer include:

• Abdominal pain in the lowe abdomen
• Blood in the stools
• Weight loss with out apparent reason
• Diarrhea, constipation, or other unusual bowel habits that do not heal
• Stools that are narrower than usual

Prevention:

Regular physical examinations rarely indicate the presence of colon cancer, which is far more curable if found and treated in its early stages. Increase risk factors of colon cancer are colorectal polyps, a family history of colon cancer, and ulcerative colitis. Regular colonoscopy examinations is a very important prevention measure especially if an individual possesses any of the above risk factors.

Treatment:

Common treatment includes removal of the lesion or part of the colon containing the tumor. Depending upon the stage of the cancers developement chemotherapy and drugs such as 5-fluorouracil may be needed. More information about the diagnosis and treatment of colon cancer can be found at MedlinPlus Medical Encyclopedia.

Gene Homologs and Protein functions:

The MSH2 gene was discovered to be a human homolog of the E. coli mismatch repair gene mutS, which supports the idea of the MSH2 genes involvement of DNA replication repair.

The MLH1 gene was identified as a frequently mutated locus in hereditary nonpolyposis colon cancer. It is a human homolog of the E. coli DNA mismatch repair gene mutL.

MSH6 also functions in damaged DNA binding and codes for a G-T binding mismatch repair protein.

Why mutations in genes necessary in all body tissues cause cancer mainly in the colon is not clear.

Information about the above genes and the function of their corresponding proteins was found using NCBI's Entrez Gene search engine.

Genes and Disease is a good source for general information on colon cancer.

Support groups:

CancerCare
Colon Cancer Network