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growths of cells that have lost their normal properties and communication with the body and have the capacity, while invading surrounding tissues, to disrupt them and produce metastases—that is, to transport themselves into other organs and tissues and form secondary tumor foci.
Malignant tumors include sarcomas, malignant tumors of connective tissue; cancer, malignant tumors that develop from epithelial tissue; and some forms of leukoses. They are found in man and animals. With the rise in average longevity in countries where medicine is highly developed, malignant tumors are diagnosed in more cases; they are the second greatest cause of death (after cardiovascular diseases).
External causes of malignant tumors may be certain radiations and chemical substances (carcinogenic substances); internal causes may be disturbances of metabolism and hormone balance. A number of tumors in animals are caused by viruses.
Treatment of malignant tumors includes surgery, radiation, and medication (and their combinations). Prophylaxis calls for decreasing the level of harmful influences on the body and the timely discovery and cure of so-called precancerous or preneoplasmic changes and early forms of malignant tumors.
L. M. SHABAD