Can You Tell if You Have Cancer by Your Poop?

Medically Reviewed on 5/5/2022

Colon Cancer

Colon cancer is the fourth most common cancer. Noticeable changes to your poop that occur with colon cancer may include blood in the stool, loose stools, hard stools, and narrow stools.
Colon cancer is the fourth most common cancer. Noticeable changes to your poop that occur with colon cancer may include blood in the stool, loose stools, hard stools, and narrow stools.

Cancer of the colon is the second most common cause of cancer death. This cancer is generally detected late when it has spread widely. The appearance of your stools and changes in your bowel habits can often give you an early warning about this cancer. What does cancer poop look like? Knowing this could help detect colon cancer early and perhaps save your life.

The first part of the colon is the ascending colon, starting from the cecum in the lower right part of your belly. Reaching your liver, it runs horizontally to the left (this part is the transverse colon). The descending colon runs down along the left side of your belly and joins the rectum in the pelvis. Cancer of the colon is also called colorectal cancer or bowel cancer. 

Colon cancer is the fourth most common cancer. Doctors rank the development of a cancer in five stages, from 0 to 4, depending on how much it has spread locally, to the lymph nodes, and distant organs in the body. Treatment is most successful in the early stages.

Many cancers are visible and easily seen. Colon cancer is deep in the body and hidden from view. You can help detect it by knowing the early signs and paying attention to the appearance of your poop.

What does colon cancer poop look like?

You should learn the visible signs of cancer found in your poop because it is often the first noticeable sign of colon cancer. There are several possible changes you may see in your poop:

Blood in the stool.

If the cancer is in the descending colon (left side) or rectum, you may see fresh, red blood in your poop. You may pass black, tarry stools if there is bleeding in the ascending colon (blood changes while passing through the colon). Blood in the stool is alarming. While it is often caused by anal fissures, hemorrhoids, and similar minor wounds to the anus and rectum, colon cancer is the most severe common cause.

Loose stools

Diarrhea often happens with colon cancer. You need to go often, and your poop is liquid or soft.

Hard stools

Constipation happens with colon cancer, and your poop may be hard and difficult to push out.

Narrow stools.

Cancer narrows the rectum. The skinny stools passed through the narrow passage are called pencil stools.

Changes in bowel habits

Changes in your usual bowel habits are important early signs of colon cancer: 

If you see a change in the appearance of stools, think about these. If you have poop that looks as described above and changes in your bowel habits, you should talk to your doctor. 

Early warning signs of colon cancer

Colon cancer is most common after 60. The early physical symptoms are often ignored. Many people believe they're a part of aging:

Risk factors for colon cancer

You should take changes in your poop's appearance, your bowel habits, and other more general signs seriously if you have one or more of these risk factors:

What's next?

What should you do if you notice the changes in your poop and the other early signs of colon cancer? You should talk to your doctor as soon as possible. They will examine you, take your risk factors into account, and evaluate the possibility of colon cancer. Your likelihood of cancer decides the course of action. 

Blood in your poop is always alarming. More than a third (33.6%) of people with blood in the stools have colorectal cancer or polyps. People with abdominal pain, a change in bowel habits, or both are also at high risk of colon cancer. If you have any of these, along with a change in your poop's appearance, your physician will likely ask for more aggressive testing.


Colorectal Cancer: Symptoms, Signs, Screening, Stages See Slideshow

Diagnosing colon cancer

Like most cancers, it's best to catch colon cancer in its early stages. Your notice of changes in your poop is the first step. Once you report it to your doctor, they will take steps to diagnose the disease:

Physical examination

Your physician will examine you for any lumps or abnormal findings in your body.

Digital rectal examination

Your physician will feel inside your rectum with a gloved finger. They can detect any lumps or unusual feel of the rectal wall. Digital rectal examination often detects cancers in the rectum.

Fecal occult blood test

You give a stool sample to the laboratory. You can easily see large amounts of blood. If the cancer produces only small amounts of blood, it is not seen (occult blood). Chemical tests can detect this blood. Two types of tests for occult blood in stools are used — guaiac and immunochemical.


A sigmoidoscope is a tube to look inside the rectum and the end of the colon. It has a light at the end and a lens for viewing. A sigmoidoscope also has tools for removing polyps or tumors or collecting biopsies.


A colonoscope is a flexible tube for looking high up inside your colon. Like a sigmoidoscope, it has a light, a lens, and tools. This test is very sensitive and diagnoses up to 72% of colon cancers.

Colonoscopy lets your physician see and remove any colon polyps, which can become cancers later. They can also remove any small cancers they see. If a part of your colon looks suspicious, your physician can take a biopsy. 

CT colonography

Computed tomography (CT) scans of the abdomen can show polyps and other abnormal findings. This procedure is also called virtual colonoscopy and can detect more than 30% of colon cancers.


Pieces of tissue are collected from abnormal appearing areas. Your physician can do this with a sigmoidoscope or colonoscope. A pathologist examines them under a microscope for signs of cancer.

DNA stool test

Your stool sample is tested for genetic changes. Some DNA changes indicate colon cancer.


Colon cancer is deadly, but detecting it early saves lives. If you notice changes in your poop's appearance, you should take it as an early warning. Pay attention to any other signs of colon cancer, and talk to your physician. Your physician will consider other things like your individual risk factors and decide what tests you need. Your alertness might save your life as detecting colon cancer early improves survival.

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Medically Reviewed on 5/5/2022

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American Cancer Society: "Colorectal Cancer Signs and Symptoms."

American Cancer Society: "Colorectal Cancer Stages."

American Journal of Gastroenterology: "Diagnostic yield of colorectal neoplasia with colonoscopy for abdominal pain, change in bowel habits, and rectal bleeding."

BMC Family Practice: "Symptoms and signs of colorectal cancer, with differences between proximal and distal colon cancer: a prospective cohort study of diagnostic accuracy in primary care."

Centers for Disease Control and Prevention: "Colorectal Cancer Screening Tests."

National Health Service: "Bowel cancer."

New York State Department of Health: "About Colorectal Cancer."