Let's Talk About Colorectal Cancer Symptoms

Signs of this disease can look like every other stomach issue you’ve ever had, making it hard to know when to worry. Here’s what the experts say are possible red flags.

by Lisa Davis Health Writer

Colorectal cancer is one scary-sounding disease—cancer that begins in either your colon and rectum is not exactly a walk in the park. Unfortunately, spotting symptoms isn’t easy, since many either look similar to run-of-the-mill issues or are mild enough they are easy to miss. If you’re concerned about colorectal cancer, here are a few things to keep an eye out for.

Colorectal Cancer Symptoms

Our Pro Panel

We went to some of the nation’s top experts in colorectal cancer to bring you the most up-to-date information possible.

Leonid Cherkassky, M.D.

Leonid Cherkassky, M.D.

Assistant Professor of Oncology

Roswell Park Comprehensive Cancer Center

Buffalo, NY

Gautam Mankaney, M.D.

Gautam Mankaney, M.D.


Cleveland Clinic

Cleveland, OH

Eduardo Vilar-Sanchez, M.D., Ph.D.

Eduardo Vilar-Sanchez, M.D., Ph.D.

Associate Professor of Clinical Cancer Prevention

The University of Texas MD Anderson Cancer Center

Houston, TX

Colorectal Cancer Symptoms
Frequently Asked Questions
What is colon cancer pain like?

Colorectal cancer frequently doesn’t cause any pain, especially in its early stages. In some cases, it can cause discomfort, like cramping or bloating, that is very similar to menstrual pain or irritable bowel syndrome. For this reason, people often miss signs that they have colon cancer.

What’s the difference between irritable bowel syndrome and colorectal cancer symptoms?

More than 10% of people worldwide have irritable bowel syndrome (IBS), which causes abdominal pain, constipation, diarrhea or both. Colorectal cancer symptoms can look virtually identical, so the only real way to know is through tests like a colonoscopy.

I’m young. Can I get colorectal cancer?

Yes. There is an increase in colon cancer in people under 50, according to the American Cancer Society. People under 55 are also nearly 60% more likely to be diagnosed with a late-stage of the disease, partly because not all doctors look for it in younger patients.

I have low iron. Should I be worried that it's a sign of colon cancer?

Anemia, or low-iron levels, can be caused by several factors. If it is persistent, your doctor will want to investigate. Along with causing significant fatigue, the condition can be a warning sign of serious illness, including colorectal cancer.

Remind Me, What Is Colon Cancer?

Colorectal cancer, often referred to as just colon cancer, is a disease that affects both your colon and rectum.

Typically, it begins as a cluster of small, noncancerous cells known as a polyp inside your intestine. Because your intestine is constantly shedding and rebuilding its lining, cells multiply rapidly here; if there is an error in the process, some of these clusters can become cancerous, eventually leading to colon cancer.

You might not have heard a ton about colorectal cancer, but every year, it kills more people than breast or prostate cancer. In fact, it’s the second most common cause of cancer deaths among men and women combined in the United States, after lung cancer.

The number one cause of colon cancer is getting older—90% of cases are diagnosed in people over age 50. Obesity, family history, and genetic disposition are other causes.

If caught early, the disease is highly treatable, which is why it’s so important to get regular screenings, especially once you turn 45.

All the Details on Colorectal Cancer

Early Diagnosis for Colorectal Cancer Matters

Unfortunately, tumors can grow without causing any noticeable symptoms—specialists in colorectal cancer are used to seeing patients who were completely blindsided by a diagnosis made when they were feeling perfectly fine.
And when the disease does trigger symptoms, it’s likely to have advanced past its earliest, most treatable, stage.

To make things even more challenging, the symptoms of colorectal cancer tend to be vague—and they can mimic sensations that you might experience on occasion anyway, even if you don’t have colorectal cancer, or any disease at all.

For instance, stomach cramps and diarrhea are symptoms of colorectal cancer, but they’re also side effects of irritable bowel syndrome or if you’re a woman, having your period. (Not to mention the result of overdoing things at a holiday meal.)

Getting screened for colorectal cancer is the only way to know for sure if you have it. Early detection matters: 90% of people diagnosed when the cancer is still limited to just the colon or rectum survive at least five years, according to the National Cancer Institute. And many of those are completely cured. But only about 39% of people with colorectal cancer are diagnosed that early, and odds of survival drop precipitously the more the cancer spreads.

What Are the Symptoms of Colon Cancer?

Even though most cases happen in people over 50, you should check in with your doc at any age if you don’t feel right.

After all, rates of colorectal cancer are increasing in people in their 40s, 30s, and even 20s, possibly because the rate of obesity (a known colon cancer risk factor) in these groups is growing.

Younger adults who develop colorectal cancer are also more likely than older people to have late-stage disease by the time they’re diagnosed, probably because they don’t even think of the problem as one to consider—and often, neither do their doctors.

Symptoms of colorectal cancer can include general, whole-body changes, as well as ones that are more obviously bowel related. They include:

  • Unexplained weight loss. If you’re losing weight without making any changes to how much you are eating or exercising, it could be a sign of a serious medical condition, including colorectal cancer, says the American Cancer Society. In fact, 40% of people with cancer say that before diagnosis they’d lost weight for no apparent reason, according to the American Society of Clinical Oncology. One reason: Cancer cells are especially metabolically active, leading your body to burn more calories.

  • Anemia. As colorectal cancer grows in your intestine, it can cause bleeding (sometimes you’ll see blood in your stool). If enough blood is lost, it can lead to low red blood cell counts—anemia—which may be picked up during a routine blood test.

  • Fatigue. Anemia and other cancer-related issues can make you feel tired or weak.

  • Blood in or on your stool. Rectal bleeding can be caused by a number of issues, including minor problems like hemorrhoids. But it can also be a symptom of colorectal cancer—in fact, rectal bleeding is the most common symptom of rectal cancer. While the blood you see when you go to the bathroom may be bright red, keep in mind that sometimes blood can make your poop look extra-dark, too.

  • Diarrhea or constipation. Who hasn’t experienced these things, right? Diarrhea and constipation are common complaints, especially if you have irritable bowel syndrome. But it’s important to always make note of them, because they can also mean that cancer is interfering with the normal functioning of your colon. If your poop routine changes drastically for no apparent reason, it’s worth having a conversation with your doctor.

  • Feeling like you still need to poop. You went to the bathroom, washed your hands, went back to your desk—and now you feel like you need to go again. If that scenario is repeating itself, you should see your doctor. Depending on where the tumor is located in your large intestine, it can make you feel like your trip to the toilet didn’t completely empty your bowels (even when it did).

  • Stool that is narrower or thinner than usual. Lots of things can affect the shape of stool, so occasional variability is nothing to worry about. But if your stool becomes narrow, especially if it gets pencil-thin, it may indicate that your colon has narrowed or become obstructed, possibly because of cancer.

  • Stomach pain or cramps, or a sensation of bloating or fullness. Many people experience stomach discomfort, even if they’re healthy. So it’s really tough to know whether this is a sign of something serious, like colon cancer, or just another random side effect of the rest of your life. Still, if the feeling is persistent or doesn’t seem right to you, it’s smart to get it checked out.

Like we said from the start, these symptoms are so vague and common, it’s really tricky to know whether they are possibly due to colorectal cancer, or just a benign side effect of your everyday life.

The most important thing to remember is that colon cancer is infinitely more treatable if you catch it before it spreads. You should never feel silly asking your doctor to check things out. It could literally be a lifesaver if it turns out to be colon cancer that you’ve caught in an early stage, and even better news if it turns out to be nothing at all.

Lisa Davis
Meet Our Writer
Lisa Davis

A health reporter and editor in New York, Lisa Davis has contributed to numerous outlets, including Health, O, the Oprah Magazine, Vogue, Science News, and others.