A colonic polyp, or visible growth, is created by the overgrowth of colonic epithelial cells. Such uncontrolled cell division is not always cancerous, but may become malignant. DNA mutations of the colonic epithelial cells—the cause of the overgrowth—may be hereditary.
lesion damage adenoma a tumor (cell mass) of gland cells alleles particular forms of genes apoptosis cell death programmed endoscopic describes procedure in which a tool is used to see within the body colectomy colon removal autosomal describes a chromosome other than the X and Y sex-determining chromosomes polyposis (FAP) and hereditary nonpolyposis colon cancer (HNPCC). These patients will usually have a specific genetic alteration.
APC. The Adenomatous Polyposis Coli (APC) gene is found on chromosome 5 and is a tumor suppressor gene. Both alleles of the gene must be inactivated for tumor growth to occur. In the normal cell, the APC gene plays a role in regulating the cycle of cellular division and replication, as well as in cell-to-cell communication, thereby suppressing tumor development. Mutations of APC result in a loss of gene function, thus allowing unregulated cellular proliferation. APC mutations are found in the majority of common colon polyps and cancers and in patients with FAP, and they may be one of the earliest genetic alterations in the adenoma-carcinoma sequence.
K-ras. The K-ras gene plays an active role in cellular signaling and promoting cell growth. The normal gene exists in both an active and inactive form. However, in the abnormal state, the active form predominates and results in a continually growth-stimulated state.
p53. The normal p53 gene is responsible for regulating cells with damaged DNA by directing abnormal cells either to halt the cycle of cell division or to die as the result of a process called apoptosis. Like APC, the p53 gene is a tumor suppressor. With the p53 mutation, the gene no longer functions, and this permits the uninhibited proliferation of cells that may have damaged DNA. p53 mutations are seen in more than half of colorectal cancers.
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