What is cancer?
All organs in the body are made of cells. Individual cells are so small, they can be seen only through a microscope. Within each cell, material called DNA stores the instructions for what the cell needs to do during its lifetime. Normally, cells divide in an orderly fashion to replace cells that have aged and died.

DNA also carries the controls that tell the cells when to stop dividing if no new cells are needed. Occasionally, damage to DNA during cell duplication may cause the controls to malfunction. Cells begin to divide uncontrollably, forming lumps or tumors.

The word “tumor” comes from a Latin word that means “swelling.”

Some tumors are made up of cells that divide excessively, but do not invade other organs. For example, a fibroid in the uterus, or a fibroadenoma in the breast are called benign, that is, non-cancerous tumors.

Malignant tumors are composed of aggressively dividing cells that destroy surrounding tissues or travel to other parts of the body. Generally, the word “tumor” refers to a malignant condition, or cancer. Each cancer is named according to where it started. So cancer that started in the colon,but has spread to the liver is still called colon cancer. Colorectal cancer is the name often used to refer to cancers that started in either the colon or the rectum.

Most cases of colon cancer arise from polyps—small growths on the lining of the colon. When they first appear, most colon polyps are benign (not cancerous), but over time some types of polyps can become cancerous.

The polyps most likely to become cancerous are the adenomas—polyps that are made of glandular cells found in the lining (the mucosal layer) of the colon. They are called adenomatous polyps.  About 95% of all cases of colon cancer develop from cells in the mucosal lining and are often referred to as adenocarcinomas.


It may take a polyp years to change from adenoma to cancer. The larger the polyp, the older it probably is, and the higher the risk that it contains a cancer. If left untreated, polyps will often become cancerous. That is why it is so important to have screening colonoscopies at regular intervals to check the colon for presence of polyps and to remove them before they become cancerous.

Colorectal Cancer
Cancer that starts in any part of the colon is called colon cancer.  If it starts in the rectum, it is called rectal cancer.  Since the treatment approaches are similar, the two cancers are jointly called colorectal cancer.

Cancer can start as a mushroom-shaped polyp, or as a flat, non-polypoid lesion on the surface of the bowel. At least half of all cases of colon cancer occur in the left side of the colon (the descending colon).

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