6 Silent Symptoms of Colon Cancer You Might Be Missing

Updated: Oct. 10, 2022

Nearly 140,000 people are diagnosed with colorectal cancer in America. Rectal bleeding is the most obvious colon cancer symptom, but other signs may be far more subtle. If you notice any of the following signs, talk to your doctor.

You learn you’re anemic

A diagnosis of anemia may be the first sign that you’re bleeding internally, even if you haven’t seen any other colon cancer symptoms. That’s particularly true for post-menopausal women. It’s not uncommon for people to bleed internally for up to six months before anything shows up in the stool, says Patricia Raymond, MD, a gastroenterologist in Virginia Beach, Virginia, and fellow at the American College of Gastroenterology. If you experience any signs of anemia, such as fatigue, skin pallor or dizziness, see a doctor; these can also be colon cancer symptoms. (Be sure you know the other signs of colon cancer in women too.)

man stopping to catch breath

You can’t catch your breath

Another side effect of a slow internal bleed is shortness of breath. If you aren’t bleeding aggressively or vomiting blood, your body puts more plasma in the blood without making more iron or red blood cells, says Dr. Raymond. This prevents you from losing blood in large volumes but reduces blood’s ability to carry oxygen, which is why you might notice shortness of breath, one of the overlooked colon cancer symptoms. (Shortness of breath may also be one of the silent signs of a heart attack.)

person trying to zip pants

You feel bloated or crampy

“If things are starting to get blocked and backed up in the colon, you may experience bloating,” says Randall F. Holcombe, MD, director of the University of Hawaii Cancer Center in Honolulu, Hawaii If you’re feeling a little puffy or crampy, there are many other factors that may be to blame, but if stomach symptoms persist, see your doctor. If you start to notice a constant pain in the right side of your abdomen, that may mean the disease in the later stages and has spread to the liver, he says. (Check out these habits that help prevent colon cancer.)

man holding stomach

You have severe constipation

A bout of constipation here and there is probably nothing to worry about, but if it becomes severe and persistent, it could be one of the symptoms of colon cancer. “This is something that is suggestive of some sort of obstruction, and if it seems to be there all the time you should get it checked out,” says Dr. Holcombe. (Read up on the best foods that cleanse your colon.)

toilet bowl

You pass skinny stool

Pay attention to what’s in the toilet, even if you don’t see blood—it can reveal lesser-known colon cancer symptoms. If your stool shape is consistently very narrow or skinny when it was previously chunkier, that could point to a restriction in the colon caused by polyps, says Dr. Raymond. Persistent diarrhea may also be one of the symptoms of colon cancer. Here are 11 things your bowel movements reveal about health.

hand on toilet flush handle

Your stool is a weird color

Bleeding from the rectum is usually red. But dark, tarry stools are also a sign there’s probably some blood in your bowel movement, and while it could be caused by something less serious, like an ulcer, this can also be one of the symptoms of colon cancer, says Dr. Holcombe. Next, don’t miss the cancer warning signs you should never ignore.