Colon cancer develops when tumorous growths develop in the large intestine. It is now the third most common type of cancer in the United States.
The colon, or large intestine, is where the body draws out water and salt from solid wastes. The waste then moves through the rectum and exits the body through the anus.
Colon cancer is also the third most common cause of cancer-related death in the U.S. In fact, in 2019, the American Cancer Society (ACS) predict that 101,420 people in the U.S. will receive a new diagnosis of colon cancer.
Healthcare professionals recommend attending regular screenings for colon cancer from the age of 50 years.
Colorectal cancer, which describes co-occurring colon cancer and rectal cancer, is also common. Rectal cancer originates in the rectum, which is the final several inches of the large intestine, closest to the anus.
In this article, we look at how to recognize and treat colon cancer, why it develops, and how to prevent it.
Colon cancer often causes no symptoms in the earliest stages. However, symptoms may become more noticeable as it progresses.
These signs and symptoms may include:
- diarrhea or constipation
- changes in stool consistency
- loose, narrow stools
- blood in the stool, which may or may not be visible
- abdominal pain, cramping, bloating, or gas
- continual urges to defecate despite passing stools
- weakness and fatigue
- unexplained weight loss
- irritable bowel syndrome
- iron deficiency anemia
If the cancer spreads to a new location in the body, such as the liver, it can cause additional symptoms in the new area.
There are different ways of assigning a stage to cancer. The stages indicate how far a cancer has spread and the size of any tumors.
In colon cancer, the stages develop as follows:
- Stage 0: Also known as carcinoma in situ, at this point, the cancer is in a very early stage. It has not grown farther than the inner layer of the colon and will usually be easy to treat.
- Stage 1: The cancer has grown into the next layer of tissue but has not reached the lymph nodes or any 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 the outer layers of the colon, and it has reached one to three lymph nodes. It has not spread to distant sites, however.
- Stage 4: The cancer has reached other tissues beyond the wall of the colon. As stage 4 progresses, colon cancer reaches distant parts of the body.
Treatment will depend on the type and stage of the colon cancer. A doctor will also take the age, overall health status, and other characteristics of the individual into consideration when deciding on the best treatment option.
The aim of treatment will be to remove the cancer, prevent its spread, and reduce any uncomfortable symptoms.
Surgery to remove part or all of the colon is called a colectomy. During this procedure, a surgeon will remove the part of the colon that contains the cancer, as well as some of the surrounding area.
For example, they will usually remove nearby lymph nodes to reduce the risk of spreading. The surgeon will then either reattach the healthy portion of the colon or create a stoma, depending on the extent of the colectomy.
A stoma is a surgical opening in the wall of the abdomen. Through this opening, waste passes into a bag, which removes the need for the lower part of the colon. This is called a colostomy.
Other types of surgery include:
- Endoscopy: A surgeon may be able to remove some small, localized cancers using this procedure. They will insert a thin, flexible tube with a light and camera attached. It will also have an attachment for removing cancerous tissue.
- Laparoscopic surgery: A surgeon will make several small incisions in the abdomen. This may be an option to remove larger polyps.
- Palliative surgery: The aim of this type of surgery is to relieve symptoms in cases of untreatable or advanced cancers. A surgeon will attempt to relieve any blockage of the colon and manage pain, bleeding, and other symptoms.
During chemotherapy, a cancer care team will administer medications that interfere with the cell division process. They achieve this by disrupting proteins or DNA to damage and kill cancer cells.
These treatments target any rapidly dividing cells, including healthy ones. These can usually recover from any chemotherapy induced damage, but cancer cells cannot.
A cancer specialist, or oncologist, will usually recommend chemotherapy to treat colon cancer if it spreads. The medicines travel through the whole body, and the treatment will take place in cycles, so the body has time to heal between doses.
Common side effects of chemotherapy include:
- hair loss
Combination therapies often use multiple types of chemotherapy or combine chemotherapy with other treatments.
Radiation therapy kills cancer cells by focusing high energy gamma rays on them. A cancer care team may use external radiation therapy, which expels these rays from a machine outside of the body.
With internal radiation, a doctor will implant radioactive materials near the site of the cancer in the form of a seed.
Some metals, such as radium, emit gamma rays. The radiation may also come from high energy X-rays. A doctor may request radiation therapy as a standalone treatment to shrink a tumor or to destroy cancer cells. It can also be effective alongside other cancer treatments.
For colon cancer, cancer care teams tend not to administer radiation treatments until the later stages. They may use them if early stage rectal cancer has penetrated the wall of the rectum or traveled to nearby lymph nodes.
Side effects of radiation treatment may include:
- mild skin changes that resemble sunburn or sun tan
- appetite loss
- weight loss
Most side effects will resolve or subside a few weeks after completing treatment.
A physician will carry out a complete physical examination and ask about personal and family medical histories.
They may also use the following diagnostic techniques to identify and stage cancer:
A doctor will insert a long, flexible tube with a camera on one end into the rectum to inspect the inside of the colon.
A person may have to follow a special diet for 24¬–48 hours before the procedure. The colon will also require cleansing with strong laxatives in a process known as bowel prep.
If the doctor finds polyps in the colon, a surgeon will remove the polyps and refer them for biopsy. In a biopsy, a pathologist examines the polyps under a microscope to look for cancerous or precancerous cells.
A similar procedure, called a flexible sigmoidoscopy, allows a doctor to examine a smaller portion of the colorectal area. This method involves less preparation. Also, a full colonoscopy may not be necessary if a sigmoidoscopy does not reveal polyps, or if they are located within a small area.
Double contrast barium enema
This X-ray procedure uses a liquid called barium to provide clearer images of the colon than a standard X-ray. A person must fast for several hours before undergoing a barium X-ray.
A doctor will inject a liquid solution containing the element barium into the colon through the rectum. They follow this with a brief pumping of air to smooth over the barium layer to provide the most accurate results.
A radiologist will then conduct the X-ray of the colon and rectum. The barium appears white on the X-ray, and any tumors and polyps will appear as dark outlines.
Following diagnosis, a doctor will determine the stage of the cancer based on the size and extent of the tumor, as well as the spread to nearby lymph nodes and distant organs.
A cancer's stage will determine the treatment options and inform the outlook.
There is no guaranteed way to prevent colon cancer. However, some preventive measures include:
- maintaining a healthy weight
- exercising regularly
- consuming plenty of fruits, vegetables, and whole grains
- limiting the intake of saturated fats and red meat
People should also consider limiting their alcohol consumption and quitting smoking.
Symptoms may not appear until the cancer has progressed. For this reason, the American College of Physicians recommend screening for people aged 50–75 years, including:
- fecal testing once every 2 years
- either a colonoscopy every 10 years or a sigmoidoscopy every 10 years plus fecal testing every 2 years
The right regularity of screening depends on an individual's level of risk. Consult a doctor for recommendations.
Usually, cells follow an orderly process of growth, division, and death. However, cancer develops when cells grow and divide uncontrollably, and when they do not die at the normal point in their life cycle.
Most cases of colon cancer originate from noncancerous tumors called adenomatous polyps. These form on the inner walls of the large intestine.
Cancerous cells may spread from malignant tumors to other parts of the body through the blood and lymph systems.
These cancer cells can grow and invade healthy tissue nearby and throughout the body in a process called metastasis. The result is a more serious, less treatable condition.
The exact causes are unknown, but colon cancer has several potential risk factors:
Colon cancer usually develops from precancerous polyps that grow in the large intestine.
The most common types of polyps are:
- Adenomas: These may resemble the lining of a healthy colon but appear different under a microscope. They can become cancerous.
- Hyperplastic polyps: Colon cancer rarely develops from hyperplastic polyps, as they are typically benign.
Some of these polyps may grow into malignant colon cancer if a surgeon does not remove them during the early stages of treatment.
Uncontrolled cell growth can occur following genetic damage or changes to DNA.
A person might inherit a genetic predisposition toward colon cancer from close relatives, especially if a family member received a diagnosis before the age of 60 years old.
This risk becomes more significant when more than one relative has developed colon cancer.
Several inherited conditions also increase the risk of colon cancer, including:
- attenuated familial adenomatous polyposis
- familial adenomatous polyposis (FAP)
- Gardner syndrome, which is a different type of FAP
- Lynch syndrome, or hereditary nonpolyposis colorectal cancer
- juvenile polyposis syndrome
- Muir–Torre syndrome, which is a variant of Lynch syndrome
- MYH associated polyposis
- Peutz–Jeghers syndrome
- Turcot syndrome, which is another variant of FAP
It is possible to have these genetic feature without developing cancer. This is because the cancer will not develop unless an environmental factor triggers it.
Traits, habits, and diet
Age is a significant risk factor for colon cancer. Around 91% of people who receive a diagnosis of colorectal cancer are over 50 years of age. However, it is becoming more common in people under 50.
As the colon is part of the digestive system, diet and nutrition play central roles in its development.
Low fiber diets can contribute. Also, according to one 2019 review, people who consume excessive amounts of the following have an increased risk:
- saturated fats
- red meat
- processed meat
Some conditions and treatments have links to an increased risk of colon cancer.
The ACS calculate a person's likely chance of survival using a 5 year survival rate.
If a cancer has not spread outside the colon or rectum, a person is 90% as likely to survive for 5 years beyond diagnosis as a person who does not have cancer.
If the cancer spreads to nearby tissues and lymph nodes, the 5 year survival rate drops to 71%. If it spreads to distant sites in the body, the rate drops to 14%.
Early detection and treatment are the most effective ways to improve the outlook for a person with colon cancer.
Where does colon cancer spread most often?
In stage 4 colon cancer (and rectal cancer), the liver is the most common site of metastasis. Colorectal cancer cells may also spread to the lungs, bones, brain, or spinal cord.Christina Chun, MPH Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.