Understanding Colorectal Cancer

Signs and Symptoms of Colorectal Cancer

This is the second article in the Understanding Colorectal Cancer Guide. This guide was developed by the HealthTree Education Team and last updated and reviewed on April 3rd, 2026. 

Colorectal cancer is a type of cancer that affects the cells lining the colon and rectum, causing them to grow and multiply too fast. This forms a tumor.

These changes often cause the first signs and symptoms of colorectal cancer. "Signs" are things that can be measured by tests, like blood in the stool. "Symptoms" are things you feel in your body, like pain or fatigue.

It is important to know that many colorectal cancers, especially in early stages, do not cause any symptoms at all. This is why regular screening is so important. Many cancers are found through routine screening before any symptoms appear.

Remember: Many of the signs and symptoms listed below can be caused by conditions other than cancer, such as hemorrhoids or irritable bowel syndrome. If you notice any changes to your health, talk to your doctor.

What are the signs and symptoms of colorectal cancer?

Changes in bowel habits

• Diarrhea, constipation, or a change in the consistency or shape of your stool that lasts more than a few days
• A feeling that your bowel does not fully empty after a bowel movement
• Stools that are narrower than usual (pencil-thin stools)

Rectal bleeding and blood in the stool

• Bright red or dark blood in the stool
• Stools that appear very dark, tarry, or black

Abdominal discomfort

• Cramping, gas, or pain in the abdomen
• A feeling of fullness, bloating, or that there is a lump or mass in the abdomen

Unexplained changes in overall health

• Unexplained weight loss
• Persistent fatigue or weakness
• Nausea or vomiting 

Signs of anemia

Because colorectal tumors can bleed slowly, some people develop anemia (a low red blood cell count) without noticing any blood in their stool. Anemia can cause:

• Fatigue and weakness
• Pale skin
• Shortness of breath

If you are experiencing any of the symptoms listed above, or notice any changes to your health that concern you, the most important thing you can do is talk to your doctor. 

Many of these symptoms have causes other than cancer, but getting checked is always the right step. And if you are not experiencing any symptoms, that is not a reason to skip screening. Finding colorectal cancer before symptoms appear gives you the best chance of successful treatment.