Colon cancer: Symptoms and signs, Causes and Risk factor, Diagnosis, Staging and Prevention

Colon cancer is cancer of the colon or large intestine which begin as small, noncancerous clumps of cells called adenomatous polyps.

Updated: June 16, 2022

Colon cancer is cancer of the colon or large intestine which begin as small, noncancerous clumps of cells called adenomatous polyps. Large intestine is the final part of your digestive tract where the body extracts water and salt from solid wastes. The waste then moves through the rectum and exits the body through the anus.
Regular screenings are recommended after the age of 50 years to help prevent colon cancer by identifying and removing polyps before they turn into cancer. Symptoms may not appear until a later stage, but gastrointestinal problems are common symptoms if they do appear. 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:

There are often no symptoms in the earliest stages, but as the cancer advances symptoms may develop. Signs and symptoms of colon cancer include:

  • A change in your bowel habits, including 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 or anemia

Additional symptoms can appear in the new area if the cancer has spread to a new location in the body. The liver is most commonly affected. Talk to your doctor if you notice any symptoms of colon cancer, such as blood in your stool or an ongoing change in bowel habits. Usually colon cancer screenings begin at age 50. But more frequent or earlier screening may be recommended your doctor if you have other risk factors, such as a family history of the disease.

Causes and Risk factor of Colon cancer:

Normally, an orderly process of growth, division, and death is followed by our body cells. Healthy cells grow and divide in an orderly way to keep your body functioning normally. Cancer happens when these cells grow and divide uncontrollably, without dying.
This is because cells continue to divide when DNA of a cell is damaged and becomes cancerous. They grow even when new cells aren't needed. As the cells accumulate, they form a tumor. Cancerous cells may spread from malignant tumors to other parts of the body through the blood and lymph systems. Overtime, the cancer cells can grow to invade and destroy normal tissue nearby and cancerous cells can travel to other parts of the body to form deposits there which is called as metastasis. This condition is more serious and less treatable.
The exact causes are unknown, but colon cancer has several potential risk factors.


Colon cancer usually develops from precancerous polyps that exist in the large intestine.
The most common types of polyps are:

  • Adenomas: These can resemble the normal lining of the colon but look different under a microscope. They can become cancerous.
  • Hyperplastic polyps: Colon cancer rarely develops from hyperplastic polyps, as they are typically benign.

If the polyps are not removed during the early stages of treatment, they may grow into malignant colon cancer over time.


Uncontrolled cell growth can happen if there is genetic damage, or if changes to the DNA affect cell division. A genetic predisposition can be inherited from family members. But most colon cancers occur in people without a family history.
Inherited gene mutations don't make cancer inevitable, but they can increase the risk of colon cancer in an an individual.
The most common forms of inherited colon cancer syndromes are:

  • Hereditary nonpolyposis colorectal cancer (HNPCC): HNPCC, also called Lynch syndrome, increases the risk of colon cancer and other cancers. People with HNPCC tend to develop colon cancer before age 50.
  • Familial adenomatous polyposis (FAP): FAP is a rare disorder that causes you to develop thousands of polyps in the lining of your colon and rectum. People with untreated FAP have a greatly increased risk of developing colon cancer before age 40.

FAP, HNPCC and other, rarer inherited colon cancer syndromes can be detected through genetic testing. Talk to your doctor if these testing are required in case you have a family history of colon cancer.
Some people are born with certain genetic mutations that make them more likely to develop cancer later in life. Sometimes, even if a person will have this genetic feature, cancer will not develop unless an environmental factor triggers it.

Traits, habits, and diet:

Age is an important risk factor for colon cancer. It increases after the age of 50.
People with sedentary lifestyles, those with obesity, and those who smoke tobacco are more likely to develop colon cancer. As the colon is part of the digestive system, diet is an important factor. Diets that are low in fiber and high in fat, calories, red meat, alcohol, and processed meats have been linked to a higher risk of colon cancer.

Underlying conditions:

Some health conditions and treatments have been associated with an increased risk of colon cancer.
These include:

  • Diabetes: People with diabetes and insulin resistance have an increased risk of colon cancer.
  • Acromegaly: This growth hormone disorder increases the risk of developing colon cancer.
  • Radiation treatment for other cancers: Radiation therapy directed at the abdomen to treat previous cancers increases the risk of colon and rectal cancer.
  • Inflammatory intestinal conditions: Chronic inflammatory diseases of the colon, such as ulcerative colitis and Crohn's disease, can increase your risk of colon cancer.

Diagnosis of Colon cancer:

Certain screening tests are recommended for healthy people with no signs or symptoms in order to look for early colon cancer as finding colon cancer at its earliest stage provides the greatest chance for a cure. People with an average risk of colon cancer can consider screening beginning at age 50. But people with an increased risk, such as those with a family history of colon cancer, should consider screening sooner.
Tests and procedures for diagnosing colon cancer include:


A long, flexible tube and slender tube attached to a video camera on one end is inserted into the rectum to view your entire colon and rectum. A special diet  may have to follow by the patient for 24 to 48 hours before the procedure. The colon will also be cleaned with strong laxatives by a process known as bowel prep. If polyps are found in the colon during the process, they are removed and sent to a pathologist for biopsy to examine under a microscope that detects cancerous or precancerous cells.

Flexible sigmoidoscopy:

This is almost similar to colonoscopy, but only a smaller portion of the colorectal area will be examined. This involves less preparation, and a full colonoscopy may not be needed if polyps are not found, or if they are located within a small area.

Double-contrast barium enema:

This is a x-ray procedure that uses a liquid called barium to provide clearer imaging results than a standard x-ray. The patient must fast for several hours before a barium enema. In this process, a liquid solution containing barium is injected into the colon through the rectum. This is followed by a brief pumping of air to smooth over barium layer for optimal results. The x-ray of the colon and rectum is then taken. The barium will appear white on the x-ray, and tumors and polyps will appear as dark outlines.
If colon cancer is detected from a biopsy, a chest x-ray, ultrasound, or CT scan of the lungs, liver, and abdomen is done to assess the spread of the cancer.

Blood tests:

No blood test can detect colon cancer. But blood test such as kidney and liver function tests is done to access your overall health. Blood test is also done to check for a substance produced by some cancer cells called carcinoembryonic antigen (CEA). The level of CEA in your blood may help your doctor understand your prognosis and whether your cancer is responding to treatment.

Staging colon cancer:

Following a diagnosis, the doctor will determine the stage of the cancer based on the size and extent of the tumor, and on the spread to nearby lymph nodes and distant organs. Staging will determine the treatment options and inform the prognosis. Staging tests may include imaging procedures such as abdominal, pelvic and chest CT scans. In many cases, the stage of your cancer may not be determined until after colon cancer surgery.
The stages of colon cancer are:

  • Stage I: The cancer has grown through the superficial lining (mucosa) of the colon or rectum but hasn't spread beyond the colon wall or rectum.
  • Stage II: The cancer has grown into or through the wall of the colon or rectum but hasn't spread to nearby lymph nodes.
  • Stage III: The cancer has invaded nearby lymph nodes but isn't affecting other parts of your body yet.
  • Stage IV: The cancer has spread to distant sites, such as other organs such as to your liver or lung.

Cancer develops progressively. Each stage is not fixed but describes a phase during which certain developments take place.

Prevention of Colon cancer:

People with an average risk of colon cancer can consider screening beginning at age 50. But people with an increased risk, such as those with a family history of colon cancer, should consider screening before the age of 50.
The type of screening and age can be decided by an oncologist after reviewing your medical history and overall health condition. The sooner it is diagnosed, better the chances of recovery.
You can take steps to reduce your risk of colon cancer by making changes in your lifestyle. These include:

  • Variety of fruits, vegetables and whole grains can be added to your diet. Fruits, vegetables and whole grains contain vitamins, minerals, fiber and antioxidants, which plays an important role in cancer prevention. Variety of fruits and vegetables can provide an array of vitamins and nutrients for your body.
  • Decrease the amount of saturated fat and red meat intake.
  • If you choose to drink alcohol, limit the amount of alcohol you drink to no more than one drink a day for women and two for men.
  • Quit smoking. Talk to your doctor about ways to quit that may work for you.
  • Exercise most days of the week. Try to get at least 30 minutes of exercise on most days. If you have been inactive, start slowly and build up gradually to 30 minutes. Also, talk to your doctor before starting any exercise program.
  • Maintain a healthy weight. If you are at a healthy weight, work to maintain your weight by combining a healthy diet with daily exercise. If you need to lose weight, ask your doctor about healthy ways to achieve your goal. Aim to lose weight slowly by increasing the amount of exercise you get and reducing the number of calories you eat.

Some medications are also available to reduce the risk of precancerous polyps or colon cancer. But these options are generally reserved for people with a high risk of colon cancer. These are not recommended for people who have an average risk of colon cancer. Regular use of aspirin or aspirin-like drug can reduce risk of polyps and colon cancer. But the dose and duration of time that would be needed to reduce the risk of colon cancer is unclear. However, taking aspirin daily has some risks, including gastrointestinal bleeding and ulcers. So doctors typically don't recommend this as a prevention strategy unless you have an increased risk of colon cancer.

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