The earliest stages of colorectal cancer have no symptoms. Colorectal tumors can grow slowly over the course of several years, which may only cause subtle symptoms at later stages. If you experience any symptoms, do not assume it is due to cancer. Many symptoms can be caused by other, less serious conditions. However, it is still important to discuss them with your doctor. Early detection and treatment improve outcomes for both cancer and other health conditions.
Symptoms will vary depending on the location of the tumor or how long it has been growing. The 2 most common symptoms of colorectal cancer are:
Changes in Bowel Habits
These may include:
- Alternating between diarrhea and constipation
- Increased frequency of bowel movements
- A feeling of incomplete bowel movements—tenesmus
- Stool that is is narrower than normal (like a pencil) or that is differently shaped than normal
- Increase in intestinal discomfort, including cramping pain, gas, and/or bloating
- Intestinal discomfort that is not relieved by bowel movements
Keep in mind that bowel habits and function are different for everyone. The changes you notice may be unique to you, but these are general changes to be aware of. If you detect changes that last at least 6 weeks, contact your doctor.
Tumors can cause bleeding, but sometimes it cannot be seen, especially if the tumor is in the first sections of the colon. If blood in the stool cannot be seen, it is called occult blood. There are specific tests that can detect occult blood in the stool.
Blood that is visible may appear as:
- Red blood from the rectum during a bowel movement without other anal symptoms, such as itching, pain, or lumps
- Stool that is streaked with red blood
- Stool that is dark, tarry, or black
It should be noted that any rectal bleeding, with or without a bowel movement, should prompt a call to your doctor. Rectal bleeding can be caused by noncancerous conditions, such as hemorrhoids, which may require medical treatment.
Later stages of cancer may cause:
- Abdominal pain or a sensation of a mass
- Obstructive rectal problems
- Decreased appetite and unintended weight loss
- Intense fatigue, abnormally low energy—anemia and iron deficiency are caused by intestinal bleeding, which reduces the red blood cell count
- Abdominal or back pain caused by pressure on nearby nerves
- Swelling in the legs, which may be caused by an obstruction in the veins or lymphatic system
- Bone pain
Colorectal cancer. American Cancer Society website. Available at: http://www.cancer.org/acs/groups/cid/documents/webcontent/003096-pdf.pdf. Accessed January 3, 2017.
Colorectal cancer. EBSCO DynaMed website. Available at:http://www.dynamed.com/topics/dmp~AN~T113642/Colorectal-cancer. Updated August 18, 2016. Accessed January 3, 2017.
Colorectal cancer. Merck Manual Professional Version website. Available at: http://www.merckmanuals.com/professional/gastrointestinal-disorders/tumors-of-the-gi-tract/colorectal-cancer. Updated July 2014. Accessed January 3, 2017.
General information about colon cancer. National Cancer Institute website. Available at: https://www.cancer.gov/types/colorectal/patient/colon-treatment-pdq. Updated June 30, 2016. Accessed January 3, 2017.
General information about rectal cancer. National Cancer Institute website. Available at: https://www.cancer.gov/types/colorectal/patient/rectal-treatment-pdq. Updated June 30, 2016. Accessed January 3, 2017.
Last reviewed December 2016 by Mohei Abouzied, MD Last Updated: 10/2/2019