Study Identifies 4 'Red Flag' Symptoms of Colon Cancer in Younger People

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  • New research has identified four “red flag” signs and symptoms associated with an increased risk of early-onset colorectal cancer.
  • Abdominal pain, rectal bleeding, diarrhea, and iron deficiency anemia were all identified as symptoms common in colorectal cancer diagnoses among people younger than 50 years old.
  • Experts are urging people with these symptoms not to delay seeking medical advice.

woman holding stomach in pain

woman holding stomach in pain

Kinga Krzeminska/Getty Images


Four “red flag” signs and symptoms have been associated with an increased risk of early-onset colorectal cancer, new research shows—an important finding as new colon cancer diagnoses in people under 50 are rising at an alarming rate.

The four symptoms—abdominal pain, rectal bleeding, diarrhea, and iron deficiency anemia—were identified in a new study, published Thursday in the Journal of the National Cancer Institute. The symptoms showed up as early as two years before a colorectal cancer diagnosis.

“Colorectal cancer is not simply a disease affecting older people,” senior investigator Yin Cao, ScD, an associate professor of surgery in the Public Health Sciences Division, and a research member of Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine said in news release.

“We want younger adults to be aware of and act on these potentially very telling signs and symptoms,” Cao added. “Particularly because people under 50 are considered to be at low risk, and they don’t receive routine colorectal cancer screening.”

How to Reduce Your Colon Cancer Risk

Rectal Bleeding, Iron Deficiency Anemia, Among the Most Concerning Symptoms

For the study, researchers at Washington University School of Medicine in St. Louis analyzed de-identified health insurance data from more than 5,000 patients with early-onset colorectal cancer, or cancer that occurs in people under the age of 50.

The aim was to identify any signs or symptoms that may help to diagnose colorectal cancer—specifically early-onset colorectal cancer—earlier, as the disease continues to become more common among younger people, and is being found at a more advanced stage. Between 1995 and 2019, the proportion of colorectal cancer cases among people ages 55 and younger increased from 11% to 20%, according to the American Cancer Society.

Researchers discovered that, in the three months to two years before receiving a diagnosis, patients who reported abdominal pain, rectal bleeding, diarrhea, and/or iron deficiency anemia had an increased risk of early-onset colorectal cancer.

The more symptoms a person had, the likelier a colorectal cancer diagnosis: A single symptom almost doubled a person’s risk of the disease; having two symptoms increased a person’s risk by more than 3.5 times, and having three or more symptoms increased the risk by more than 6.5 times.

For some, symptoms showed up as many as two years before diagnosis. About 19% of patients experienced their first symptom in the three months to two years before being diagnosed; nearly 50% of patients saw their first sign or symptom within three months of a diagnosis.

Two symptoms in particular—rectal bleeding and iron deficiency anemia—indicate an urgent need for further screening, through endoscopy, Cao said in the news release.

Location of Colorectal Cancer May Influence Symptoms

The four “red flag” symptoms are likely linked to where colorectal cancers form in the colon and rectum, particularly among younger people.

“The majority of colon cancer in younger patients is on the left side of the colon,” said Anton Bilchik, MD, PhD, chief of medicine and director of the Gastrointestinal and Hepatobiliary Program at Saint John’s Cancer Institute in Santa Monica, California. “If it’s on the left side, the bleeding may be more obvious and anemia may be more obvious as opposed to the cancer being on the right side.”

Recent research has shown too that there’s been a shift to left-sided tumors, as early-onset colorectal cancer diagnoses become more common. The proportion of rectal cancers specifically has increased from 27% in 1995 to 31% in 2019, despite better efficacy at preventing left-sided colorectal cancer through screening.

“We do think of cancers in the lower parts of the colon as more likely to cause symptoms, because the stool is more formed—there’s less liquid—and bleeding is more likely to show up on toilet paper or in the toilet as red,” Alan Harzman, MD, a colorectal surgeon with The Ohio State University Wexner Medical Center, told Health. “Bleeding from colon cancers farther up, though, tends to mix in with the stool and be less noticeable.”

Signs and Symptoms of Colon Cancer

Any 'Red Flag' Symptoms Necessitate Discussion With a Healthcare Provider

Younger people, particularly those who have not yet reached colorectal cancer screening age, are likelier to brush off any of these digestive symptoms—a decision that may also be contributing to an increase in advanced-stage disease.

“Most of these patients have them for years and blow them off as hemorrhoids because they look up their symptoms online and assume they can’t get cancer,” Ashkan Farhadi, MD, a gastroenterologist at MemorialCare Orange Coast Medical Center in Fountain Valley, California, told Health.

But patients aren’t the only ones who need to know these important signs and symptoms. “It’s also crucial to spread awareness among primary care doctors, gastroenterologists and emergency medicine doctors,” Cao said in the news release. “To date, many early-onset colorectal cancers are detected in emergency rooms, and there often are significant diagnostic delays with this cancer.”

If you experience any of these “red flag” symptoms, it’s important to bring them up to your healthcare provider sooner rather than later.

“Since the majority of early-onset colorectal cancer cases have been and will continue to be diagnosed after symptom presentation, it is crucial to recognize these red-flag signs and symptoms promptly and conduct a diagnostic work-up as soon as possible,” Cao said in the news release. “By doing so, we can diagnose the disease earlier, which in turn can reduce the need for more aggressive treatment and improve patients’ quality of life and survival rates.”

Aside from colorectal cancer, the standout symptoms could also be an indicator of another gastrointestinal health issue that needs to be addressed, like inflammatory bowel disease (IBD) or irritable bowel syndrome (IBS).

“It would be very unusual for a young person to have pain, diarrhea, and rectal bleeding and not have something going on,” Dr. Bilchik said. “That could be IBS, cancer, or something else. Either way, don’t ignore your symptoms, even if you’re younger.”