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Colon Cancer Symptoms and Diagnosis

In its early stages, colon cancer often does not cause signs or symptoms. Colon cancer symptoms usually appear after the polyps develop into malignant tumors. This is why, it is important to have regular screening tests, especially after the age of 50, to detect colon cancer early when it is more easily treated.

Common symptoms of colon cancer include:

  • Changes in bowel habits, such as constipation or frequent diarrhea
  • Blood in your stools
  • Persistent abdominal discomfort, such as cramps, gas or pain
  • Loss of appetite
  • Weakness or fatigue
  • Unexplained weight loss

If you experience the above symptoms and your symptoms last for several weeks, see your doctor immediately to discuss your concerns and arrange for tests to get to the bottom of your symptoms.

How is Colon Cancer Diagnosed?

Your doctor will likely begin by asking about your symptoms and performing a physical examination. During the physical exam, your doctor will press on your abdomen to see if there is any discomfort or masses present. Your doctor will also perform a digital rectal exam (DRE), in which, inserting a gloved, lubricated finger into your rectum to check for any abnormalities and to test your stool for blood.

In addition to a physical examination, the following tests may be used to diagnose colon cancer.


Colonoscopy uses a long, flexible and slender tube attached to a video camera and monitor to view your entire colon and rectum. If any suspicious areas are found, your doctor can pass surgical tools through the tube to take tissue samples (biopsies) for analysis and remove polyps.


A biopsy is the removal of a small amount of tissue for examination under a microscope. Other tests can suggest that cancer is present, but only a biopsy can make a definite diagnosis of colon cancer.

A biopsy may be performed during a colonoscopy, or it may be done on any tissue that is removed during surgery. Sometimes, a CT scan or ultrasound is used to help perform a needle biopsy. A needle biopsy removes tissue through the skin with a needle that is guided into the tumor.

The polyps and samples are then sent to a laboratory to be analyzed under a microscope to check for cancer cells. If cancer is found, more lab tests may be performed on the biopsied sample, like tests that look for gene changes in the cancer cells. Results of these tests can help oncologists determine what treatments may work best or not at all.

Blood test

A blood test can count red blood cells to determine if there’s bleeding in the intestine, a common symptom of colon cancer. It also can measure levels of a protein called carcinoembryonic antigen (CEA). Higher levels of CEA may indicate that a cancer has spread to other parts of the body.

Imaging tests

Imaging tests use x-rays, magnetic fields, sound waves, or radioactive substances to create images of the inside of your body. The imaging tests used to look for colon cancer include:

  • Chest X-ray
  • Computer tomography (CT) scan
  • Magnetic resonance imaging (MRI)
  • Ultrasound
  • Positron emission tomography (PET) scan (not as commonly used)

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