Colorectal cancer is cancer that develops in the colon or rectum. Depending on where these cancers begin, people may also refer to them as colon or rectal cancer.

Most colorectal cancers start as a polyp, which is a growth on the inner lining of the colon. Some types of polyps can change into cancer over time, but not all polyps become cancer.

According to the American Cancer Society, colorectal cancer is the third most common cancer in the United States, excluding skin cancer.

Colorectal cancer may not cause any symptoms in its early stages when the cancer is small. Signs and symptoms often appear once a tumor has grown or spread into surrounding tissues or organs.

Colorectal cancer symptoms
  • constipation
  • diarrhea
  • narrow stools
  • feeling of not being empty after a bowel movement
  • rectal bleeding
  • blood in the stool
  • black stools
  • abdominal bloating
  • abdominal pain
  • rectal pain or pressure
  • a lump in the abdomen or rectum
  • decreased appetite
  • nausea or vomiting
  • anemia
  • fatigue
  • weakness
  • unintentional weight loss
  • bowel obstruction
  • bowel perforation

Cancer that has spread to other parts of the body may cause other symptoms, such as:

  • bone pain (if cancer has spread to the bones)
  • jaundice (if cancer has spread to the liver)
  • shortness of breath (if cancer has spread to the lungs)

Many of the symptoms of colorectal cancer can also be due to other conditions. Still, it’s important to speak with a doctor as soon as possible if you experience any of the above symptoms.

If a person has symptoms of colorectal cancer or has had an abnormal screening test, a doctor will generally recommend exams and tests to find the cause.

For people with an average chance of developing colorectal cancer, the American College of Physicians recommends screening with one of the following options:

  • a colonoscopy every 10 years
  • a fecal immunochemical test (FIT) or high sensitivity guaiac-based fecal occult blood test (gFOBT) every 2 years
  • a flexible sigmoidoscopy every 10 years plus an FIT every 2 years

Individuals who have a higher chance of developing colorectal cancer should talk with a doctor about the method and frequency of screening that’s best for them.

Try this risk calculator to learn your own risk level.

If tests detect cancer, the person will undergo further testing to stage the cancer and plan the best course of treatment.

Medical history and physical exam

A doctor will typically ask about your medical history to determine whether you have any risk factors, such as a family history of colorectal cancer. They’ll also ask about your symptoms and how long you’ve had them.

A physical exam involves feeling the abdomen for masses or enlarged organs and possibly performing a digital rectal exam (DRE).

During a DRE, a doctor inserts a gloved finger into the person’s rectum to check for abnormalities.

Fecal tests

A doctor may recommend tests to check for blood in a person’s stool. Blood in the stool is not always visible to the eye. These tests help detect blood that people can’t see.

People perform these tests, which include an FOBT or FIT, at home using a kit that the doctor will provide. The kit allows them to collect one to three samples of stool for analysis.

Blood tests

Doctors may order blood tests to check for signs of colorectal cancer such as anemia, which occurs when you have too few red blood cells.

A doctor may also order liver function tests and tests to look for tumor markers, such as carcinoembryonic antigen and CA 19-9. Blood tests alone cannot diagnose colorectal cancer.

Signoidoscopy

A sigmoidoscopy, also called a flexible sigmoidoscopy, allows a doctor to look inside the sigmoid colon. This procedure is less invasive than a full colonoscopy. Doctors may recommend it if a colonoscopy is not possible for any reason.

Colonoscopy

A diagnostic colonoscopy is a test a doctor orders because someone has symptoms of a condition involving the colon or another screening test detected an abnormality. They use this test to view the entire length of the colon and rectum.

Doctors perform this test using a colonoscope, which is a thin, flexible tube with a camera on the end. They insert this tube into the body through the anus.

Doctors can also pass special instruments through the colonoscope to remove polyps and take tissue samples for a biopsy.

Proctoscopy

A proctoscopy involves inserting a proctoscope through the anus. A proctoscope is a thin, rigid tube with a camera on the end that allows doctors to view the inside of the rectum. Doctors may use it to check for cancer or other conditions in the rectum.

Biopsy

A biopsy is a lab test that involves examining a sample of tissue. Doctors usually remove polyps or suspicious areas of tissue for investigation during a colonoscopy, but they can also remove them during a surgical procedure if needed.

The doctor sends the removed tissue to a lab where specialists examine it under a microscope. If cancer is present, the specialists may also test the samples for gene changes or perform other lab tests to help doctors classify the cancer.

Imaging tests

Imaging tests can allow doctors to:

  • view suspicious areas that might be cancerous
  • check how far cancer has spread
  • check if treatment is working
Diagnostic imaging tests

Imaging tests that may help doctors diagnose colorectal cancer include:

The best way to prevent colorectal cancer is by having regular colorectal cancer screening tests if you fit the criteria for screening.

Polyps can take as many as 10 to 15 years to develop into cancer. Screening can help doctors find and remove polyps before they turn into cancer or find cancer early, before it has spread to other parts of the body. This can mean it is easier to treat.

The 5-year relative survival rate for early stage colorectal cancer that hasn’t spread is 91.5%.

The United States Preventive Services Task Force recommends that people ages 45 to 75 years receive screening for colorectal cancer. Those between 76 and 85 years can ask their doctor if they should undergo screening. Doctors also recommend that some groups undergo early screening (see details in the box below).

Who needs early screening?

People who may undergo screening before they are 45 years old include those who:

Certain factors may increase the risk of colorectal cancer. (See the “What are the risks for colorectal cancer?” section below.) Research has also identified some protective factors, such as:

  • exercise
  • aspirin
  • polyp removal

Along with regular screening, avoiding risk factors and increasing protective factors may help prevent colorectal cancer.

Some lifestyle factors, such as smoking, can increase the risk of colorectal cancer.

Other risk factors are unavoidable, such as family history and age.

Risk factors for colorectal cancer

Risk factors for developing this condition include:

  • being:
    • over 50 years old
    • of American Indian, Alaska Native, African American, or Ashkenazi Jewish descent
  • having:
    • overweight or obesity
    • a family history of colorectal cancer
    • a personal history of IBD, adenomatous polyps, or colorectal cancer
    • certain genetic syndromes, such as Lynch syndrome
    • type 2 diabetes
  • having the following lifestyle factors:

Treatment for colorectal cancer depends on:

  • the cancer’s stage
  • the location of cancer in the body
  • where the cancer has spread, if applicable

Your doctor will discuss your treatment options, possible side effects, and the benefits of each treatment with you when creating a treatment plan.

Colorectal cancer treatment

Doctors may use one or a combination of the following treatments to treat colorectal cancer:

  • surgery
  • radiofrequency ablation or cryoablation
  • radiation therapy
  • chemotherapy
  • targeted therapies, such as anti-angiogenesis therapy, epidermal growth factor receptor inhibitors, and immunotherapy

The outlook for a person with colorectal cancer will depend on a number of factors, such as:

  • the stage of the cancer
  • characteristics of the cancer
  • treatments options and response

Their overall health and other medical conditions they may have also play a role.

Only a doctor familiar with their situation can determine what their outlook is likely to be based on these predictive factors and statistics. Even then, it’s impossible to tell exactly how an individual will respond to treatment.

Survival rates are very high among people with colorectal cancer that doctors have detected and treated early.