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Neoplasia is a disease process that results in over 100 different malignant diseases that share a common biology and natural history. Any cell in the body that can undergo mitosis or cell division can be affected. Cancer has links to other disease processes. Some infections cause cancer: e.g. schistosomiasis associated with bladder cancer and the liver fluke, Clonorchis sinensis, which causes cancer of the gall bladder. There are also toxic causes: e.g. mesothelioma, a tumor arising in the pleura which lines the thoracic cavity resulting from exposure to asbestos (asbestosis). Despite popular opinion, however, it is unlikely that local trauma is a cause of cancer.
As a fundamental disorder of cellular growth and differentiation or development, cancer is essentially a genetic disorder at the cellular level. Most tumors are encapsulated and benign in behavior. Occasionally they may create symptoms from cosmetic or mass effects. In using the generic word “cancer”, however, we are concerned here with malignant tumors that are morphologically abnormal under the microscope. They show uncontrolled growth leading to local invasion with disruption of tissues, and later metastasis or spread to loco-regional lymphatics and later the blood stream. Cancer kills mostly through blood-borne metastasis.