Colon cancer happens when tumorous growths develop in the large intestine. It is the third most common type of cancer in the United States.
The colon, or large intestine, is where the body extracts water and salt from solid wastes. The waste then moves through the rectum and exits the body through the anus.
It is also the third most common cause of cancer-related death, and in 2017, 95,520 new diagnoses are expected to occur in the United States (U.S.). However, advances in diagnosis, screening, and treatment have led to steady improvements in survival.
Regular screenings are recommended after the age of 50 years.
Colon cancer and rectal cancer may occur together. This is called colorectal cancer. Rectal cancer originates in the rectum, which is the last several inches of the large intestine, closest to the anus.
Fast facts on colon cancer:
Here are some key points about colon cancer. More detail is in the main article.
Colon cancer affects the large intestine and it usually starts with polyps in the wall of the intestine.
Symptoms may not appear until a later stage, but if they do, gastrointestinal problems are common symptoms.
Treatment involves a combination of chemotherapy, radiation therapy, and surgery, possibly resulting in a colostomy.
A healthy lifestyle with a high-fiber, low-fat diet can help prevent colon cancer, and screening can detect it in the early stages.
Symptoms and signs
Colon cancer affects the large intestine. It usually develops from benign polyps.
There are often no symptoms in the earliest stages, but symptoms may develop as the cancer advances.
diarrhea or constipation
changes in stool consistency
loose and narrow stools
rectal bleeding or blood in the stool
abdominal pain, cramps, bloating, or gas
pain during bowel movements
continual urges to defecate
weakness and fatigue
unexplained weight loss
irritable bowel syndrome (IBS)
iron deficiency anemia
If the cancer spreads to a new location in the body, additional symptoms can appear in the new area. The liver is most commonly affected.
There are different ways of staging cancer. The stages depend on how far the cancer has spread.
Here is a brief summary of a commonly used four-stage account of where the cancer is at the beginning of each stage.
Stage 0: The cancer is in a very early stage. It is known as carcinoma in situ. It has not grown further than the inner layer of the colon.
Stage 1: The cancer has grown into the next layer of tissue, but it has not reached the lymph nodes or other organs.
Stage 2: The cancer has reached the outer layers of the colon, but it has not spread beyond the colon.
Stage 3: The cancer has grown through outer layers of the colon and it has reached one to three lymph nodes. It has not spread to distant sites.
Stage 4: The cancer has reached other tissues beyond the wall of the colon. As stage 4 progresses, the cancer reaches distant parts of the body.
Cancer develops progressively. Each stage is not fixed but describes a phase during which certain developments take place.
Surgery for colorectal cancer often means a person will need a colostomy. A bag collects waste from a stoma, bypassing the need for the lower part of the large intestine.
Surgery to remove part or all of the colon is called a colectomy. The surgeon removes the part of the colon containing the cancer and the surrounding area.
Nearby lymph nodes are also usually removed. The healthy portion of the colon will either be reattached to the rectum or attached to a stoma depending on the extent of the colectomy.
A stoma is an opening made in the wall of the abdomen. Waste will pass into a bag, removing the need for the lower part of the colon. This is called a colostomy.
Some small, localized cancers can be removed using endoscopy.
Laparoscopic surgery, using several small incisions in the abdomen, may be an option to remove larger polyps.
Palliative surgery may relieve symptoms in cases of untreatable or advanced cancers. The aim is to relieve any blockage of the colon and manage pain, bleeding, and other symptoms.
Chemotherapy administers chemicals that interfere with the cell division process by damaging proteins or DNA in order to damage and kill cancer cells.
These treatments target any rapidly dividing cells, including healthy ones. The healthy cells can usually recover from any chemically-induced damage, but cancer cells cannot.
Chemotherapy is generally used to treat cancer that has spread because the medicines travel through the whole body. Treatment occurs in cycles, so the body has time to heal between doses.
Common side effects include:
Combination therapies often mix multiple types of chemotherapy or combine chemotherapy with other treatments.
Radiation treatment damages and kills cancer cells by focusing high-energy gamma-rays on them.
Radioactive gamma-rays are emitted from metals such as radium, or from high-energy x-rays. Radiotherapy can be used as a standalone treatment to shrink a tumor or destroy cancer cells, or alongside other cancer treatments.
Radiation treatments are not often used until a later stage. They may be employed if early stage rectal cancer has penetrated the wall of the rectum or traveled to nearby lymph nodes.
Side effects may include:
mild skin changes resembling sunburn or suntan
appetite and weight loss
Most side effects resolve a few weeks after completing treatment.