The body is made up of trillions of living cells. Normal body cells grow, divide, and die in an orderly way.
During the early years of a person’s life, normal cells divide faster to allow the person to grow. After the person becomes an adult, most cells divide only to replace worn-out, damaged, or dying cells.
Cancer begins when cells in a part of the body start to grow out of control. Cancers start because of out-of-control growth of abnormal cells.
Cancer cell growth is different from normal cell growth. Instead of dying, cancer cells keep on growing and form new cancer cells. Unlike normal cells, these cancer cells can grow into other tissues. In most cases, the cancer cells form a tumour, but some cancers, like leukaemia, rarely form tumours. Instead, these cancer cells are in the blood and bone marrow.
When cancer cells get into the bloodstream or lymph vessels, they can travel to other parts of the body. There they begin to grow and form new tumours that replace normal tissue. This process is called metastasis. No matter where a cancer may spread, it is always named for the place where it started. For instance, breast cancer that has spread to the liver is still called breast cancer, not liver cancer.
Colorectal cancer is a cancer that starts in the colon or the rectum.
Colon and rectal cancers begin in the digestive system, also called the gastrointestinal system. The digestive system processes food for energy, and the last part of it (the colon and rectum) absorbs fluid to form solid waste (stools) that then passes from the body. In order to understand colorectal cancer, it helps to know something about the structure of the digestive system and how it works.
Swallowed food travels to the stomach. There it is partly broken down, liquefied and sent to the small intestine. The small intestine also breaks down the food and absorbs nutrients.
The liquid is then passed on to the large intestine (also called the colon). The colon absorbs water and nutrients from the liquid and also serves as a storage place for waste matter. The waste moves from the colon into the rectum, the last six inches of the digestive system. From there the waste passes out of the body through the opening called the anus.
The wall of the colon and rectum is made up of layers of tissues. Colorectal cancer starts in the inner layer and can grow through some or all of the other layers. The stage (extent of spread) of a cancer depends to a great degree on how deep the cancer goes into these layers.
Cancer that starts in these different areas may cause different symptoms. Colon cancer and rectal cancer have many things in common. Most colorectal cancers develop slowly over many years.
We now know that most of these cancers start as a polyp – a growth of tissue that starts in the lining and grows into the centre of the colon or rectum. A type of polyp, known as an adenoma, can become cancer. Removing a polyp early may keep it from becoming cancer. Over 95 per cent of colon and rectal cancers that begin this way are adenocarcinomas, starting as polyps in the lining of the colon and rectum.
Dr. Darley Solomon is a general surgeon at Chrissie Tomlinson Memorial Hospital in the Cayman Islands. This article is the first in a weekly series during March, which is Colorectal Cancer Awareness Month.
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