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.

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.

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

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.

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.

Sigmoidoscopy

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.

Colonoscopy

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.

Biopsy

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.