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Tumor is a descriptive term for a growth or mass of cells that are independent of the physiologic function or demand of their surrounding structures. The 2 characteristic biologic growth patterns of tumors include the ability to (1) disrespect tissue boundaries and invade other structures (invasiveness) and (2) gain access to blood and lymph vessels or other structures to spread tumor cells to distant locations and allow these specially equipped cells to survive and grow new remote tumors (metastases). If a tumor does not have either property, it is benign; if a tumor can invade locally but even at a large size does not have a tendency to metastasize, it is called semimalignant; and if a tumor has the ability to metastasize once a sufficient size is reached, it is a malignant tumor.
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Colorectal lesions may be classified as benign, potentially malignant, or malignant based on their pathologic features (Table 49-1); the semimalignant variant with invasion only but no affinity to later form of metastases is not common in the colon. The overwhelming majority of colorectal tumors are of epithelial origin and arise from the mucosal surface, where they become visible descriptively as a polyp. Benign polyps include nonneoplastic polyps (eg, hyperplastic, hamartomatous, or inflammatory polyps); the potentially malignant group consists of adenomatous polyps. Once dysplastic cells in a polyp cross the boundaries of the mucosa (basement membrane and muscularis mucosae) and start to invade the submucosa and the muscularis mucosae, a true cancer (carcinoma) with the potential to metastasize is established. Tumors of nonepithelial or mesenchymal origin are comparably rare and include, among others, lipoma, lymphoma, carcinoid, and sarcoma.1-3
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Colonic tumors are important for 2 reasons. First, they are frequent and account for both a significant mortality rate as well as ...