Updated: July 24, 2018
Colorectal cancer is any cancer that affects the colon and the rectum. It is also known as bowel cancer, colon cancer, or rectal cancer. The term colorectal describes this area that begins at the colon and ends at the anus. These cancers can also be named colon cancer or rectal cancer, depending on where they start. Colon cancer and rectal cancer are often grouped together because they have many features in common.
Cancer starts when cells in the body start to grow out of control. Colorectal cancer may be benign, or non-cancerous, or malignant. A malignant cancer can spread to other parts of the body and damage them.
Symptoms of colorectal cancer include:
Colorectal cancers can often bleed into the digestive tract. Sometimes the blood can be seen in the stool or make it look darker, but often the stool looks normal. Over time, the blood loss can build up and can lead to anemia. Sometimes a blood test showing a low red blood cell count is an indication of colorectal cancer.
Many of these symptoms are similar to that of infection, hemorrhoids, or irritable bowel syndrome. So a proper diagnosis is required for right treatment.
The colon and rectum is a part of the large intestine which is part of the digestive system, also called the gastrointestinal (GI) system. Most of the large intestine is made up of the colon which is a muscular tube about 5 feet long. The parts of the colon are named by which way the food is traveling through them.
The ascending and transverse sections together are called the proximal colon where as the descending and sigmoid colon are called the distal colon. The colon absorbs water and salt from the remaining food matter after it goes through the small intestine. The waste matter that is left after going through the colon goes into the rectum where it is stored until it passes out of the body through the anus. A ring shaped sphincter muscles around the anus keeps stool from coming out until they relax during a bowel movement.
Most colorectal cancers start as a growth on the inner lining of the colon or rectum which are called polyps. Over time these polyps can change into cancer, but not all polyps become cancer. The chance of a polyp changing into cancer depends on the type of polyp it is. The types of polyps can be:
Factors that can make a polyp more likely to increase the risk of developing colorectal cancer include:
If cancer forms in a polyp, overtime it can grow into the wall of the colon or rectum. The wall of the colon and rectum is made up of many layers. Colorectal cancer starts in the innermost layer called the mucosa and can grow outward through some or all of the other layers. From the wall, the cancer can grow into blood vessels or lymph vessels and can travel to nearby lymph nodes or to distant parts of the body. The stage or extent of spread of a colorectal cancer depends on how deeply it grows into the wall and if it has spread outside the colon or rectum.
Factors for which your chance of getting a disease such as cancer is called as risk factor. Different cancers have different risk factors. Some risk factors, like smoking, can be changed. Others, like age of a person or family history, can't be changed.
But having a risk factor, or even many, does not necessarily mean that you will get the disease. And some people who get the disease may not have any known risk factors. Several risk factors are found that might increase the chance of developing colorectal polyps or colorectal cancer of an individual. Some of these can be changed where as others can not.
Many lifestyle related factors such as diet, weight, and exercise have been linked to colorectal cancer.
People who develop colorectal cancer have inherited gene changes that cause family cancer syndromes and can lead to them getting the disease.
Several risk factors are found to associated with colorectal cancer, but it is not yet clear exactly how all of these factors might cause this cancer.
Usually a cancer is caused by changes in the DNA inside our cells. DNA is the chemical in our cells that makes up our genes, which control the way our cells function. As our parents are the source of our DNA, we usually look like them. But DNA affects more than just appearance.
Some genes help control when our cells grow, divide into new cells, and die. The genes that help cells grow, divide, and stay alive are called oncogenes. Genes that help keep cell division under control or cause cells to die at the right time are called tumor suppressor genes. Cancers can be caused by DNA mutations that turn on oncogenes or turn off tumor suppressor genes leading to uncontrolled growth of cells.
When DNA mutations are passed on in families, it is called as inherited mutations. Colorectal cancers can be caused by inherited gene mutations which are rare. Many of these DNA changes and their effects on the growth of cells are now known. For example:
Discussing genetic testing with a qualified cancer genetics professional before any genetic testing is recommended.
These are the most gene mutations that lead to cancer where these DNA changes affect only cells that come from the original mutated cell. They happen during lifetime of a person and does not not passed on to their children. Certain risk factors probably play a role in causing these acquired mutations.
In most of the cases, the first mutation occurs in the APC gene which leads to an increased growth of colorectal cells because of the loss of brake on cell growth. Further mutations may then occur in other genes, which can lead the cells to grow and spread uncontrollably. Other unknown genes are probably involved as well.