Figure 15-1 General scheme for development of a carcinoma in an epithelial tissue such as colonic epithelium. The diagram shows progression from normal epithelium to local proliferation, invasion across the lamina propria, spread to local lymph nodes, and final distant metastases to liver and lung.
Cancer is not a single disease but rather comes in many forms and degrees of malignancy. There are three main classes of cancer:
• Sarcomas, in which the tumor has arisen in mesenchymal tissue, such as bone, muscle, or connective tissue, or in nervous system tissue;
• Carcinomas, which originate in epithelial tissue, such as the cells lining the intestine, bronchi, or mammary ducts; and
• Hematopoietic and lymphoid malignant neoplasms, such as leukemia and lymphoma, which spread throughout the bone marrow, lymphatic system, and peripheral blood.
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