What is Cancer?
Cancer has been known since human societies first learned to record their activities. It was well known to peoples of ancient civilizations. The word CANCER means CRAB in the Greek language. The founder of modern medicine, Hippocrates, likened the spreading of a cancerous tumor to the shape of the claw of a crab. This description best describes cancer even today. Cancer is a disease involving dynamic changes in the genome. The pathway to tumor formation is a multi-step journey involving the accumulation of genetic alteration along the way. Mutations are responsible for oncogenes with dominant gain of function and tumor suppressor gene with recessive loss of function; both classes of cancer genes have been identified through their alteration in human and animal cancer cell and by the elicitation of cancer phenotype in experimental models.
In normal life, cells are always exposed to carcinogens in one form or the other, but they don't always turn cancerous. These carcinogens because they can repair the damage do this. Faulty genes are repaired and it takes more than just a single gene to cause cancer. Also, the body's immune system (the body's defense mechanism) destroys any abnormal cell, thus preventing its multiplication. As we age, our defense system weakens and thus cancer is more common in the elderly. There is also accumulation of enough number of faulty genes to cause damage. Undiagnosed cancers also reach their peak during old age and hence we see more cases of cancer in older people.
What causes cancer?
Cancer is caused by several factors. These can be classified into the following:
- Tobacco smoking
- Spicy diet
- Occupational hazards like chimney sweepers
- Hormone producing tumors
Formation of a cancerous tumor
The single cell containing the abnormal oncogene multiplies quickly. It divides to form two cells, which in turn divides to form four cells, then eight and so on. Each and every cell of the tumor then has the ability to turn cancerous. Tumor growth is measured by the time taken for the number of cells in a tumor to double. This period usually varies from about 1 month to 2 years. A patient usually detects a solid tumor after 25 to 30 such doublings. In this phase the tumor contains approximately billion cells and has a diameter of half an inch.
What is a cancerous tumor?
A cancerous tumor is a collection of many abnormal cells, most of which divide without any control. This tumor spreads to neighboring tissues by forcing its way between normal cells. The abnormal cells of the tumor bear little or no resemblance to the cells of their origin. They are irregular in size and shape.
What does the cancerous tumor consist of?
The cancer cell has a large nucleus. They may also consist of calcium deposits that can be seen on an X-ray. These characteristic coupled with the irregular appearance of the cells are often the diagnostic feature of the detection of cancer.
How does cancer spread?
A cancerous tumor spreads not only locally but also migrates to different sites in the body by a process called as metastasis.
The tumor cells multiply and proliferate to form outgrowths from the original tumor. These cells then spread to the surrounding tissue. The involvement of nerve fibers near the spreading tumor causes pain. The spread of cancer can be considered in the blood as well as the lymphatic fluid. Spread of cancer in the lymphatic fluid. As the tumor grows it spreads into the neighboring lymphatic vessels. The cancer cells detach from the primary tumor and are carried by the lymphatic flow until they settle in a lymph node. In the lymph node the cancer cell again starts dividing to form another tumor. The tumor then remains in the node. It is temporarily stopped from spreading by the immune cells in the lymphatic system. The tumor soon overcomes the immune system and may spread throughout the body in the same manner.
Spread of cancer in the blood
Cancer cells mostly spread to organs having a good blood supply. These organs are the liver, lungs, bones and brain. The growing tumor invades nearby blood vessels by growing into their walls. A cancer cell detaches itself from the primary tumor. This cancer cell flows with blood until it lodges itself in a very small blood vessel called as a capillary. Here it starts forming a secondary tumor.
The spread of the cancer from one site to a distant site is by a process called as metastasis. Cancerous cells become detached from the primary tumor. The blood or lymphatic system carries these to distant sites like the liver, lungs, bones and brain. The cancer cell then proliferates as these sites to form secondary tumors or secondaries.
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