Metastasis dissemination or spread of malignant cells

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Metastasis- dissemination or spread of malignant cells from the primary tumor to distant sites by direct spread of tumor cells to body cavities or through lymphatic and blood circulation (a) Tumors growing in or penetrating body cavities may shed cells or emboli that travel within the body cavity and seed the surface of other organs ii) Lymphatic Spread (1) Transport of tumor cells through the lymphatic circulation (2) Most common mechanism of metastasis (3) Tumor emboli enter lymph by way of the intestinal fluid (4) Malignant cells may also penetrate lymphatic vessels by invasion (5) After entering lymph, malignant cells either lodge in the lymph nodes or pass b/n the lymphatic and venous circulation 28
(6) Tumors arising in areas of the body with rapid and extensive lymphatic circulation are at high risk for metastasis through lymph channels (a) Breast cancer iii) Hematogenous Spread (1) Dissemination of malignant cells via the bloodstream (a) Directly related to vascularity of tumor (2) Malignant cells that do survive (not all survive due to turbulence of arterial circulation, insufficient oxygenation, or destruction by the body’s immune system) are able to attach to endothelium and attract fibrin, platelets, ad clotting factors to seal themselves from immune system (a) Endothelium retracts, allowing malignant cells to enter basement membrane and secrete enzymes (i) Implantation occurs iv) Angiogenesis (1) Growth of new blood vessels from the host tissue stimulated by the release of growth factors (2) Rapid formation of new blood vessels help malignant cells obtain necessary nutrient and oxygen (3) The vessels formed are abnormal and function ineffectively (a) Through this network, tumor emboli can enter systemic circulation and travel to other sites d) Carcinogenesis – cancer causing i) Viruses and bacteria (1) After infecting individuals, DNA viruses insert a part of their own DNA near the infected cell genes causing cell division (a) Newly formed cells now carry viral DNA (2) Examples (a) Human papilloma virus (HPV) -> cervical and head and neck cancers (b) Hepatitis B (HBV) -> liver cancer (c) Epstein-Barr Virus (EBV) -> Burkitt lymphoma and nasopharyngeal cancer (3) Bacteria (a) H. pylori associated with increased incidence of gastric malignancy related to chronic superficial gastritis, w/resultant atrophic and metaplastic changes to gastric mucosa ii) Physical Agents (1) Sunlight (a) Increased risk for skin cancer in fair skinned people (2) Radiation (a) Repeated diagnostic x-ray procedures (b) Radiation therapy used to treat disease iii) Chemical Agents (1) Most hazardous chemicals produce their toxic effects by altering DNA structure in body sites distant from chemical exposure (2) Example (a) Tobacco iv) Genetics and Familial Factors (1) Cancer with underlying genetic abnormalities (a) Burkitt lymphoma (b) Malignant melanoma (2) Familial: hallmarks of families with a hereditary cancer syndrome include cancer in two or more first degree or second- degree relatives, early onset of cancer in family members younger than 50, same type of cancer in several family

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