Colorectal cancer is cancer that develops in the colon or rectum. Depending where they begin, these cancers may also be referred to as colon cancer 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, though 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

If the cancer has spread to other parts of the body, you may experience other symptoms. For instance:

  • 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 be caused by other conditions. Still, you should see your doctor as soon as possible if you experience any of the above symptoms.

If you have symptoms of colorectal cancer or have had an abnormal screening test, your doctor will 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
  • flexible sigmoidoscopy every 10 years plus FIT every 2 years.

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

Try this risk calculator to learn your own risk level.

If colorectal cancer is found, further testing is required to stage the cancer and plan the best course of treatment.

Medical history and physical exam

Your doctor will ask you about your medical history to determine if you have any risk factors, such as a family history of colorectal cancer. You’ll also be asked about your symptoms and how long you’ve had them.

A physical exam entails feeling your abdomen for masses or enlarged organs, and possibly having a digital rectal exam (DRE) done.

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

Fecal tests

Your doctor may recommend tests to check for blood in your stool. Blood in the stool is not always visible to the eye. These tests help detect blood that cannot be seen.

These tests, which include an FOBT or FIT, are performed at home using a kit provided. The kit allows you to collect one to three samples of your stool for analysis.

Blood tests

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

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


A sigmoidoscopy, also called a flexible sigmoidoscopy, allows your doctor look inside your sigmoid colon. This procedure is less invasive than a full colonoscopy, and it may be recommended if a colonoscopy is not possible for any reason.


When a colonoscopy is performed because you’re having symptoms or an abnormality was found during a screening test, it’s called a diagnostic colonoscopy.

The test is used to view the entire length of your colon and rectum.

It’s performed using a thin, flexible tube with a camera on the end called a colonoscope that’s inserted into the body through the anus.

Special instruments can be passed through the colonoscope to remove polyps and remove tissue samples for a biopsy.


A proctoscopy involves inserting a proctoscope through the anus. A proctoscope is a thin, rigid tube with a camera on the end that’s used to view the inside of the rectum. It’s used to check for cancer in the rectum.


A biopsy is a lab test that examines a sample of tissue. Polyps or suspicious areas are usually removed during a colonoscopy, but they can also be removed during a surgical procedure if needed.

The tissue is sent to a lab where it’s examined under a microscope. If cancer is found, the samples may also be tested for gene changes. Other lab tests may be performed to help classify the cancer.

Imaging tests

Imaging tests can be used to:

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

Imaging tests that may be used to help diagnose colorectal cancer include:

The best way to prevent colorectal cancer is by having regular screenings.

Colorectal cancer screening tests look for cancer or precancer even though you have no symptoms. Polyps can take as many as 10 to 15 years to develop into cancer.

Screening allows doctors the opportunity to find and remove polyps before they turn into cancer.

Screening also helps find colorectal cancer early and before it has spread to other parts of the body so that it may be easier to treat.

The 5-year relative survival rate for early stage colorectal cancer that hasn’t spread is approximately 90 percent.

The U.S. Preventive Services Task Force recommends that people age 50 to 75 years be screened for colorectal cancer and those between ages 76 and 85 years ask their doctor if they should be screened.

Who needs early screening?

Some people are advised to begin screening earlier than 50 years old. These include people who:

Certain factors have been shown to increase the risk of colorectal cancer.

Some protective factors have also been identified, such as:

  • exercise
  • aspirin
  • polyp removal

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

There are certain factors that increase your risk for colorectal cancer. Some risks can be avoided, such as certain lifestyle choices like smoking. Other risks cannot be avoided, such as family history and age.

Risk factors for colorectal cancer
  • over 50 years old
  • family history of colorectal cancer
  • personal history of adenomatous polyps or colorectal cancer
  • genetic syndromes, such as Lynch syndrome
  • personal history of IBD
  • type 2 diabetes
  • of African American or Ashkenazi Jews descent, which is likely due to healthcare inequities placing them at the highest risk
  • alcohol use
  • cigarette smoking
  • overweight or having obesity
  • sedentary lifestyle
  • red meat and processed meat consumption
  • meat preparation at very high temperatures

Treatment for colorectal cancer depends on:

  • location
  • stage
  • where the cancer has spread

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

Colorectal cancer treatment

One or a combination of the following treatments may be used to treat colorectal cancer:

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

The outlook for colorectal cancer is dependent on a number of factors, such as the:

  • stage of the cancer
  • characteristics of the cancer
  • treatments
  • response to treatment

Your overall health and other medical conditions also play a role.

Only a doctor familiar with your situation can arrive at a prognosis based on these predictive factors and statistics. Even then, it’s impossible to tell exactly how an individual will respond to treatment.

When detected and treated early, the outlook for colorectal cancer is excellent based on survival rates.