Tumours A tumour is a mass of new tissue growth that does not react to normal controls or the organizing influence of other tissues, and it has no useful function in the body. This applies to both types of tumours, malignant and benign. Malignant, also known as, cancerous tumours, are additionally defined by their invasion of local tissue and their ability to spread to other parts of the body. Benign Tumours A benign tumour which is not cancerous, is less serious than malignant tumours because they do not spread to other parts of the body, but they may cause damage by local growth and pressure on other structures, producing serious complications such as bleeding. Benign tumours generally grow slowly and kill the host only if it occupies or attaches to an organ so as to interfere with a critical function. The cells of benign tumours closely resemble the cells of the tissue of origin.
Surface benign tumours include warts and moles. Malignant Tumours A malignant tumour always kills (unless treated) because of its invasive and metastatic characteristics. The tumour grows locally by spreading into surrounding tissues. Solid tumours, which develop in the breast, colon, lung, and other organs, contain an inner core with high pressure zones that compress and collapse blood vessels, often preventing the penetration of blood-borne cancer treatments. It spreads to distant sites by the breaking off of malignant cells, which move through the blood and lymphatic systems, attach themselves, and begin to grow as new colonies.
Malignant tumours are diagnosed by examination of their vascularity, shapes, forms of cells division, and differentiation. More than a hundred different types have been identified in humans. In general, those derived from epithelial tissue are carcinomas, and those from connective tissue are sarcomas. The most common form of malignant tumour of the respiratory tract is lung cancer, which began increasing in frequency at an alarming rate about 1940. In 1980 it was the leading cause of cancer deaths in men and is also rapidly increasing in woman.
It is attributed to cigarette smoking and environmental pollution: cancer of the lung is rare in nonsmokers, and exposure to materials such as asbestos, chromium, and radioactive substances increases the probability of developing lung cancer. Malignant tumours, also known as lymphomas, one of the main types of lung cancer, arise in the lymph nodes related to the lungs and other body tissue. the other main type of lung cancer is Sarcomas, it may originate in the lungs or in some other structure such as a bone. Sarcomas have a poor prognosis, but recent advances in the treatment of lymphomas have increased the long term survival. The factors controlling tumour growth are poorly understood, although genetics seems to play a role Tumours in laboratory animals may be transplanted to a second host using only a single tumour cell.
This suggests that only one normal cell needs to become cancerous for tumour growth to begin. Tumours have been experimentally induced in animals by chemical, physical, and viral agents, and by radiation. Cancer researchers no longer believe that a single drug will be able to cure cancer. Experts now believe that a combination of drugs will be the best method to kill tumours. One route being researched utilizes antibodies that bind to specific receptors on the tumour cell, thereby inhibiting tumour growth by blocking certain tumour-growth factors from entering the cell. Tumour necrosis factor (TFN), an immune-system protein, has been found effective in cutting off the blood supply to tumours, although too much TFN causes severe side effects. The work of physician Francis Peyton Rous, gave rise to the virus theory of the causes of cancer.
In 1960, Rous found that he could transmit a cancerous tumour (sarcoma) from one hen to another by using an injection of tumour filtrate. The sarcoma virus was the first tumour virus identified, and it opened up a whole new area of cancer research. Rous shared the 1966 Nobel Prize for physiology or medicine for his work.