Colon Cancer Symptoms That Are Easily Overlooked

The critical role of colon cancer screening

Often people with colon cancer have no symptoms initially. That’s why screening is so important.

Colon cancers start as polyps, or clumps of cells, in the lining of the colon — the final part of the digestive tract. These visible growths are present for years before they transform into cancer, says Dr. David S. Weinberg, chair of the department of medicine and chief of the section of gastroenterology at Fox Chase Cancer Center in Philadelphia. He notes that polyps provides a window of opportunity for cancer prevention and early detection.

Using a colonoscopy — which relies on a long, flexible tube with a digital camera called a colonoscope — or another screening method, clinicians can find and remove polyps before colon cancer develops or detect cancer at an early asymptomatic stage. This greatly increases the likelihood of successful treatment that allows the vast majority of patients with stage 1 cancer — when the malignancy is confined to the colon — to survive their cancer.

Know your colon cancer risk.

For people of average risk, the U.S. Preventive Services Task Force, a panel of national experts, recommends beginning colon cancer screening at 50, while the American Cancer Society suggests starting this at age 45. The Centers for Disease Control and Prevention notes that about 90% of colorectal cancer (malignancies starting in the colon or rectum) occur in people 50 and older.

More recently, for reasons that aren’t exactly clear, colon cancer has been increasing among young adults under the normal screening age. That’s drawn more attention to need to assess individual patient risk.

Discuss with your doctor if you should begin screening earlier — and when — if you have elevated risk of colon cancer, such as if you have a family history of colon cancer or Lynch syndrome, an inherited syndrome associated with a higher risk of certain cancers, including colon cancer.

Nonspecific symptoms

When it’s not detected by screening, colon cancer can advance and become much more difficult to effectively treat. Besides a lack of obvious signs in the early stages, colon cancer symptoms, when they exist, tend to be nonspecific — like abdominal pain — and may be caused by a variety of issues.

While clinicians are careful not to be alarmist, they’re also strident in counseling patients to be evaluated for symptoms — whether those turn out to be cancer or not.

If someone hasn’t yet been screened for colon cancer and develops symptoms that can’t be explained by any other cause, that person should be evaluated a physician urgently, says Dr. Emil Lou, a gastrointestinal oncologist at M Health Fairview and assistant professor of medicine in the division of hematology, oncology and transplantation at the University of Minnesota. The following are symptoms that may be associated with colon cancer.

Blood in the stool

Cancers can cause slow gastrointestinal bleeding. Rectal bleeding or blood in the stool is sometimes associated with colon cancer — though as with other symptoms, there are many causes. A person may notice bright red blood with rectal bleeding or that, when they go to the bathroom, their stool is darker-colored due to blood.

“In young patients, blood in stool may be attributed to a benign condition like hemorrhoids, as cancer tends to occur mostly in older individuals,” says Dr. Priyanka Kanth, a colon cancer specialist at Huntsman Cancer Institute and an associate professor of internal medicine at the University of Utah. This may lead to a delay in the diagnosis if it’s not investigated further. As such, Kanth recommends having a low threshold for investigating “red flag” symptoms, even in young patients.


Along with blood in stool, anemia is another possible symptom related to gastrointestinal bleeding. With anemia — low red blood cell count — there aren’t enough healthy red blood cells to carry oxygen to the rest of the body.

“A subtle finding, in that it can take many months to develop, is a slowly decreasing blood count” — i.e. becoming anemic — or evidence of iron deficiency that occurs for the same reason, Weinberg says.

Anemia may be diagnosed with a blood test, such as a complete blood count that measures parts of the blood. That includes the presence of hemoglobin, the iron-rich component in blood that carries oxygen throughout the body. Anemia can cause a person to feel fatigued, though it’s not always accompanied by symptoms.

Persistent abdominal pain or discomfort

There are many causes of stomach or abdominal discomfort, from food intolerance to viruses, points out Dr. Tomislav Dragovich, chief of the hematology-oncology and clinical research divisions at Banner MD Anderson Cancer Center in Gilbert, Arizona. “Colon cancer is not the most common cause of abdominal pain — far away from that thankfully.”

And yet persistent abdominal pain, cramping or discomfort is sometimes a sign of this deadly cancer. Either way, experts say, you should be evaluated by a medical professional to get to the bottom of it.

Cancer occurring in adults under 50, or early-onset colorectal cancer, has a higher risk of being discovered at a later stage — and becoming metastatic — and being more aggressive, says Lou, who is also the medical director of the Masonic Cancer Center clinical trials office at the University of Minnesota.

For that reason, along with paying attention to other listed symptoms, “any unusual or new forms of pain in the abdomen or chest, shortness of breath or pain in the bones can potentially represent metastatic spread of colorectal cancer to the liver, lungs or bones, respectively,” Lou says.

Constipation or diarrhea

A change in bowel habits — constipation or diarrhea — that persists is another symptom that can be related to many other things, but which can also be a symptom of colon cancer.

If you notice that you have severe constipation or your stool consistency has changed, and the problem seems to continue unabated when you take steps to address it, like making dietary changes, it may be time to speak with your doctor.

With colon cancer, large tumors can block the colon. Conversely, chronic constipation may be associated with a higher risk of developing colorectal cancer, according to some research, including a study published in Clinical Epidemiology last year. One speculated reason for this is that when it takes longer for bowel movements, it may increase the contact of bile acids or other carcinogens in stool with the gut wall.

Unintended weight loss

Cancer growth may affect metabolism. In addition, tumor growth and any related stomach discomfort may impact a person’s appetite. Any or all of those factors can contribute to weight loss.

If you’ve shed pounds — and aren’t trying to — particularly if it can’t be explained by other more obvious causes, like a change in diet or exercise, make sure to let your doctor know in order to evaluate possible causes of unintended weight loss.

Extreme fatigue

A variety of factors can leave a person feeling fatigued or weak. Some of those may relate to other symptoms that person may experience with colon cancer, like anemia or changes in metabolism that not only cause a person to lose weight when they aren’t trying to but decrease energy as well.

As with other possible colon cancer symptoms, this one is very far from clear cut — as it could be due to many other non-cancer related issues. Still, as with any persistent health issue, it shouldn’t be ignored.

“In general,” Kanth reminds, “if you have blood in your stool, a feeling that you bowels don’t empty all the way, unexplained weight loss or lack of appetite, change in bowel habits, unexplained ongoing abdominal pain or feelings of extreme fatigue, then you should consult your doctor.”

6 possible symptoms of colon cancer

— Blood in the stool.

— Anemia.

— Persistent abdominal pain or discomfort.

— Constipation or diarrhea.

— Unintended weight loss.

— Extreme fatigue.

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