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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 – 2 – 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

- 3 – 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.


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