Early Symptoms of Colon Cancer

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At first, people with colon cancer might have no symptoms. That’s why routine screenings are so important. Knowing the early symptoms of colon cancer is important, too.

Symptoms of colon cancer may vary from one person to the next. It all depends on the size of the tumor and where it is located in the large intestine. But, it's time to see your doctor if you notice any of the following:

  • Changes in bathroom habits
  • Bloody stools
  • Anemia symptoms like fatigue
  • Belly pain

Changes in Bathroom Habits

Colon cancer can affect your bowel habits. You may develop diarrhea. Or, the opposite could happen and you may feel constipated. Many otherwise healthy people also experience these conditions. If they last for more than a few days, see your doctor.

Colon cancer can also change the shape of your stools. They may appear narrower than usual. Your bowels may never feel empty—even after you’ve gone to the bathroom. You could also lose control of your bowels, which means you have bowel movements when you’re not trying.

Bloody Stools

Colon cancer can lead to bloody stools. Bleeding from cancerous tumors in the colon can make stool look very dark or even black. Tumors may not bleed very much, or they may bleed continuously. Bleeding could stop and start. Sometimes a chemical test is the only way to know if there is blood in your stool. This is called a fecal occult blood test.

It’s important to know that blood in the stool is not always a sign of colon cancer. Other conditions involving the digestive tract can cause bloody or black, tarry stools. Hemorrhoids and Crohn's disease are two examples.

Certain foods can also change the color of your stool. For instance, eating beets can make stool look red or even black. Eating more foods or supplements rich in iron can have the same effect.

If you think there's blood in your stool, don’t hesitate to see your doctor. Your doctor can confirm or rule out the presence of blood and or additional tests to determine its cause.


In time, bleeding caused by colon cancer can lead to a condition called anemia. That's when you have too few red blood cells. Red blood cells carry oxygen to all parts of your body. If you have a shortage of these cells, you might feel overly tired. You could also have shortness of breath and feel sluggish. If you have anemia, rest doesn’t ease your symptoms.

For symptoms of anemia, your doctor can order a blood test to determine if your red blood cell count is low.

Belly Pain

Colon cancer may cause unusual belly pain or discomfort. You may also experience other nagging symptoms, like cramps, gas and bloating. Healthy people may have these issues from time to time. For someone with colon cancer, however, the pain is persistent and does not go away.

Other early signs of colon cancer include weight loss and vomiting. If you're losing weight without trying, check in with your doctor. Vomiting without an obvious reason, such as stomach flu, is always a cause for concern. Both of these could signal something serious like colon cancer.

You know your own body the best. When something is amiss, see your doctor. Keep track of your symptoms and be prepared with some details, such as how long you’ve noticed them. This information helps your doctor determine next steps towards a diagnosis.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Feb 8
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.

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