Benign tumours generally grow slowly and kill thehost only if it occupies or attaches to an organ soas to interfere with a critical function. The cells ofbenign tumours closely resemble the cells of thetissue of origin. Surface benign tumours includewarts and moles. Malignant Tumours A malignanttumour always kills (unless treated) because of itsinvasive and metastatic characteristics.
The tumourgrows locally by spreading into surroundingtissues. Solid tumours, which develop in thebreast, colon, lung, and other organs, contain aninner core with high pressure zones that compressand collapse blood vessels, often preventing thepenetration of blood- borne – 2 – cancertreatments. It spreads to distant sites by thebreaking off of malignant cells, which movethrough the blood and lymphatic systems, attachthemselves, and begin to grow as new colonies. Malignant tumours are diagnosed by examinationof their vascularity, shapes, forms of cells division,and differentiation. More than a hundred differenttypes have been identified in humans. In general,those derived from epithelial tissue arecarcinomas, and those from connective tissue aresarcomas.
The most common form of malignanttumour of the respiratory tract is lung cancer,which began increasing in frequency at an alarmingrate about 1940. In 1980 it was the leading causeof cancer deaths in men and is also rapidlyincreasing in woman. It is attributed to cigarettesmoking and environmental pollution: cancer of thelung is rare in nonsmokers, and exposure tomaterials such as asbestos, chromium, andradioactive substances increases the probability ofdeveloping lung cancer. Malignant tumours, alsoknown as lymphomas, one of the main types oflung cancer, arise in the lymph nodes related to thelungs and other body tissue.
the other main type oflung cancer is Sarcomas, it may originate in thelungs or in some other structure such as a bone. Sarcomas have a poor prognosis, but recentadvances in the treatment of lymphomas haveincreased the long term survival. The factorscontrolling tumour growth are poorly understood,although genetics seems to play a role Tumours in- 3 – laboratory animals may be transplanted to asecond host using only a single tumour cell. Thissuggests that only one normal cell needs tobecome cancerous for tumour growth to begin. Tumours have been experimentally induced inanimals by chemical, physical, and viral agents,and by radiation.
Cancer researchers no longerbelieve that a single drug will be able to curecancer. Experts now believe that a combination ofdrugs will be the best method to kill tumours. Oneroute being researched utilizes antibodies that bindto specific receptors on the tumour cell, therebyinhibiting tumour growth by blocking certaintumour-growth factors from entering the cell. Tumour necrosis factor (TFN), an immune-systemprotein, has been found effective in cutting off theblood supply to tumours, although too much TFNcauses severe side effects. The work of physicianFrancis Peyton Rous, gave rise to the virus theoryof the causes of cancer.
In 1960, Rous found thathe could transmit a cancerous tumour (sarcoma)from one hen to another by using an injection oftumour filtrate. The sarcoma virus was the firsttumour virus identified, and it opened up a wholenew area of cancer research. Rous shared the1966 Nobel Prize for physiology or medicine forhis work. Science