Although colon cancer may not cause obvious symptoms, especially in its earlier stages, it can cause changes in your bowel habits, blood in your stool, and other unusual symptoms.

Colon cancer develops when malignant cells grow in your large intestine, also known as your colon. Sometimes, colorectal cancers — which affect both your colon and rectum — are also called colon cancer.

Here’s what you need to know about some of the most common symptoms of colon cancer and when you should contact a doctor.

What’s the difference between colorectal cancer and anal cancer?

Cancers are named after the location of the body where they first develop.

Colorectal cancers are malignancies in the colon and rectum. Anal cancer affects the anus, which is the lowest part of your gastrointestinal (GI) system. For reference, your rectum is the connecting point between your colon and anus.

About 20% of people with anal cancer may not have symptoms. But if symptoms do occur, they may be slightly different to those of colorectal cancer. Anal bleeding is possible, but other common symptoms include anal pain or itching, constipation, and lymph node swelling near your groin.

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Colon cancer can cause changes to your stool, especially its appearance. You may notice that your stool is narrower than normal, and it may be harder to pass.

Another possible symptom of colon cancer is blood in your stool. This can cause stool to look dark brown or black. Rather than seeing blood on the outside of the stool, you may see discoloration throughout your passed stool.

At what stage does colon cancer bleed?

Bloody stool from colon cancer is due to a buildup of blood in your digestive tract. You might notice darker stool that contains blood, and you may also start experiencing anemia due to blood loss. Anemia is when you have a deficit of red blood cells.

Colon cancer may not cause bleeding at first. If the cancer has spread to your rectum, however, you may notice bright red blood after a bowel movement, as well as blood covering the outside of your stool.

Colon cancer may also change your bowel habits and movements. Rather than having an occasional loose or hard stool, you may instead experience such changes that last longer than a few consecutive days.

For example, you might experience:

Other GI symptoms of colon cancer may include:

In later stages, colon cancer can spread to your liver. If this is the case, you may experience symptoms of jaundice, such as yellowing of the whites of your eyes or your skin.

Age is one common risk factor for colon cancer. The chance goes up after the age of 50 years. For this reason, a doctor may recommend a colon cancer screening around the age of 45 years.

However, earlier screenings may be warranted if you have other risk factors for colon cancer. These include a personal or family history of:

Certain lifestyle factors may also increase your chance of colon cancer development, including:

  • eating a diet low in fiber but high in fats
  • not eating enough fruits and vegetables
  • living a sedentary lifestyle
  • drinking alcohol
  • smoking

When doctors detect them early, up to 90% of colorectal cancers are curable. In fact, a doctor may discover colon cancer through a regular screening test before it even causes symptoms.

That said, it’s important to contact a doctor for a diagnosis if you experience the above symptoms for longer than 2 weeks. Although these could be related to other GI issues, such as IBD, a doctor should rule out colon cancer.

If you’ve already received a diagnosis of colon cancer, it’s still important to speak with a doctor if you start experiencing any of the above symptoms or if they’re getting worse. Symptoms of colorectal cancer tend to develop once the cancer has spread.

When you’re experiencing GI symptoms associated with colon cancer, treatment will consist of targeting the cancer itself.

The exact treatment depends on how large the cancer is and whether it’s spread to the rectum, lymph nodes, or other areas of the body.

Possible treatment options include:

Learn more about the treatment of colon cancer.

Colon cancer starts in your large intestine. It often doesn’t cause noticeable symptoms until it’s spread to nearby areas, such as the rectum.

It’s important to contact a doctor to rule out colon cancer if you’re experiencing any unusual symptoms, including bowel changes or blood in your stool. The earlier a doctor begins to treat colon cancer, the better your overall outlook.

Regular screenings are important in detecting possible colon cancer.