These ‘Red Flag’ Symptoms Are the Most Common Warning Signs of Colorectal Cancer in Younger People

New research has identified two “red flag” symptoms that show up in nearly half of all early-onset colorectal cancer cases: abdominal pain and hematochezia, or blood in the stool. 

In the U.S., colorectal cancer is more common among older people—the average diagnosis is age 66. However, the incidence of early-onset colorectal cancer—which refers to cases diagnosed in people under age 50—is rising and has doubled since the 1990s. 

The review—published in JAMA Network Open on May 24—looked at 81 studies that included data from over 24 million people younger than 50. They found that, in both the U.S. and globally, people with early-onset colorectal cancer most often presented with blood in their stool, abdominal pain, and altered bowel habits. 

“The challenge always is: what sort of symptoms can be associated with the potential risk of a cancer?” Kishore Guda, PhD, DVM, an associate professor at the Case Western Reserve University Comprehensive Cancer Center, told Health. “What this paper, at a minimum, kind of emphasizes is if you find something abnormal, go and get checked.”

Here’s what experts had to say about the study and how identifying signs of colorectal cancer can protect your health.

With colorectal cancer incidence rising in younger people, researchers wanted to identify any common symptoms in this age group that might otherwise be missed or brushed off. 

To do this, reviewers examined 81 studies that were conducted in various regions around the globe. Together, these studies included data from nearly 25 million people. 

The authors found that 45% of people with early-onset colorectal cancer presented with hematochezia, also known as rectal bleeding or bloody stool, and about 40% of patients said they had abdominal pain. The third most common early-onset colorectal cancer symptom (affecting 27% of people) was altered bowel habits, which the study defined as constipation, diarrhea, alternating bowel habits, or alternating diarrhea and constipation. 

Rectal bleeding and abdominal pain were also both associated with a greater likelihood of having colorectal cancer than not having it, the review found. 

Across 34 studies, the reviewers found that it took about four to six months after symptom onset for patients to get diagnosed with early-onset colorectal cancer.

These findings aren’t necessarily novel—a study published just over a year ago investigated 5,075 early-onset colorectal cancer cases and identified four “red flag” symptoms. These included abdominal pain, rectal bleeding, diarrhea, and iron deficiency anemia. But the new research pooled data from thousands more people and further emphasizes just how important it is for younger people to recognize warning signs of the disease.

The review didn’t explicitly look into why it took so many months for people to get diagnosed with colorectal cancer, even after they’d been experiencing symptoms. However, the authors noted that the issue could lie both with younger people and physicians.

The average person under 50 may not think to seek care when they first start experiencing these symptoms, or may be deterred by logistical issues such as finding childcare or accessing healthcare, Yi-Qian Nancy You, MD, professor of surgery and director of the Young-Onset Colorectal Cancer Program at the University of Texas MD Anderson Cancer Center, told Health.

“Individuals who are younger, they’re not even thinking cancer,” said Guda. “They’re like, ‘I’m just 35 or 40, why would I get cancer? I don’t have any family members with a cancer—why would I suspect that? I’m just going to wait.’”

On the other hand, physicians could also be contributing to the problem—healthcare providers may assume that symptoms are signs of something less serious. 

“The frontline providers, whether it’s ER physicians or a primary care physician, it’s really hard to fault them for not immediately triggering a cancer workup,” You told Health. “Sometimes it does take a second visit or a repeated symptom before a workup is triggered.”

The good news is that most of the time, both skeptical patients and doctors are correct: Abdominal pain and blood in the stool are often signs of other conditions, such as diverticulitis in the colon, hemorrhoids, or inflammatory bowel disease, Guda explained.

But assuming that these symptoms are no big deal or delaying treatment can put your health at risk.

Generally speaking, all people—regardless of age—should know to look out for the following colorectal cancer symptoms:

• Blood in your stool
• Changes in bowel habits, including constipation and diarrhea 
• Stomach cramps, bloating, or discomfort
• Unexplained weight loss 
• Vomiting
• Fatigue 

Again, because these symptoms are fairly non-specific, they’re not a sure sign that someone has colorectal cancer. But if something feels off, Guda said, it’s best to bring it up with a doctor.

This is especially important because, by the time someone has symptoms of colorectal cancer, the case could be a bit more serious. 

“Young patients present at a little bit later stage, so two-thirds of them are already stage three or stage four by the time they’re diagnosed,” said You. “That may or may not translate to a tumor that’s a little more symptomatic.”

The U.S. Preventive Services Task Force recommends people start getting screened for colorectal cancer at age 45. People with a high genetic risk for colorectal cancer may start getting regular colonoscopies even earlier. But in general, “there are no particular guidelines” for finding asymptomatic colorectal cancer in younger people, Guda explained.

“How do we identify people who are at a higher risk of early-onset colorectal cancer? There is not an easy answer,” he said.

If someone is experiencing one of these symptoms, there’s no need to panic, experts emphasized.

“It’s really hard to take a symptom as a stand-alone red flag to trigger a whole massive workup for cancer,” said You. “We can’t just go 100% over to the other end of the spectrum.”

However, if stomach pain, bowel changes, or other issues persist—especially if you’re experiencing more than one—you shouldn’t ignore it, You explained.

If someone is experiencing some of these symptoms, they can try using an at-home stool test to check for colorectal cancer, Guda suggested. But again, having a healthcare provider assess your symptoms is the best course of action. If necessary, they can help screen you for colorectal cancer via a colonoscopy or some other test. 

In general, there’s a higher chance that someone will recover from cancer when it’s caught early and treated early. 

“You know your body well,” said Guda. “If you have anything like [these symptoms], just go and get it checked. Get a workup, get a colonoscopy, try to rule in or rule out things, and do it quickly, too.”