This Warning Sign Linked to 8.5 Times Higher Risk

• Researchers say that rectal bleeding is a strong indication of early onset colorectal cancer in adults under 50.
• Experts say younger adults who experience this symptom should undergo a colonoscopy to screen for colorectal cancer.
• Rates of early onset colorectal cancer in young adults have been rising for more than a decade.

Rectal bleeding is a telltale sign that young adults under 50 may have colorectal cancer, according to a new study.

Researchers reported that rectal bleeding in younger adults increases the odds of a colorectal cancer diagnosis by 8.5 times.

The scientists reached their conclusions after analyzing 443 patients under 50 who underwent a colonoscopy at the University of Louisville Health System, KY, between 2021 and 2023.

Of the participants, 195 were diagnosed with early-onset colorectal cancer while 248 subjects had clear colonoscopy results.

The researchers said 88% of the young cancer patients underwent a colonoscopy because of symptoms, not because of routine screenings.

They added that 70% of the cancer patients had no family history of the disease.

In addition, people who had smoked in the past were more than two times as likely to develop early onset colorectal cancer as people who hadn’t smoked.

The researchers’ study was presented this week at the American College of Surgeons Clinical Congress 2025 in Chicago. The findings have not been published yet in a peer-reviewed journal.

The scientists said their research shows that young adults as well as medical professionals should take rectal bleeding as a significant sign of colorectal cancer.

“Many of the early-onset colorectal cancers that I see have no family history,” said Sandra Kavalukas, MD, a colorectal surgeon at the University of Louisville School of Medicine and a senior author of the study, in a press statement. “This research lends support to the question of who does or doesn’t warrant a colonoscopy: if you have a person below the screening age with rectal bleeding, you should seriously consider a colonoscopy.”

Experts interviewed by Healthline who were not involved in the study agreed with this assessment.

“Young people with rectal bleeding should get a colonoscopy,” said Alan Venook, MD, a professor of medical oncology and the associate director of program development at the Helen Diller Family Comprehensive Cancer Center at the University of California San Francisco.

“The hardest message to get across is that colorectal cancer is a disease of young people,” he added.

Alan Bilchik, MD, a surgical oncologist and chief of medicine and the director of the Gastrointestinal and Hepatobiliary Program at Providence Saint John’s Cancer Institute in Santa Monica, California, said medical professionals should no longer assume that rectal bleeding in younger adults is caused by hemorrhoids.

“Colorectal cancer is a young person’s disease,” he told Healthline. “We can no longer take for granted symptoms such as rectal bleeding in young adults.”

Robert Smith, MD, a senior vice president of early cancer detection science at the American Cancer Society, agrees.

“Doctors often downplay symptoms of colorectal cancer in younger adults, believing that the chances of the symptoms being caused by colorectal cancer are remote because the patient is too young,” Smith told Healthline. “The study results are not surprising. Persistent rectal bleeding is not normal and the source should be immediately investigated.”

Nilesh Vora, MD, a medical oncologist and medical director of the MemorialCare Todd Cancer Institute at Long Beach Medical Center in California, said the research is an important reminder to people under the age of 50.

“Don’t ignore any symptoms,” he told Healthline. “This research sends this message a little louder.”

The American Cancer Society (ACS) estimates there will be more than 150,000 new cases of colorectal cancer diagnosed in the United States this year.

More than 100,000 of those cases will be colon cancer, while slightly less than 50,000 will be rectal cancer.

The diagnoses are split almost evenly between males and females.

Colorectal cancer is the third-leading cause of cancer-related deaths in men and the fourth leading cause in females in the United States. It’s the second most common cause of cancer deaths overall. Colorectal cancer is expected to cause about 53,000 deaths this year.

The Cancer Society reports that the rate of people being diagnosed with colorectal cancer in the United States has been declining about 1% per year since the mid-1980s. They credit early screening and changes in lifestyle habits.

However, they note that the downward trend is mostly occurring in older adults. In people under 50, the rate of colorectal cancer diagnosis increased more than 2% per year between 2012 and 2021.

The death rate from colorectal cancer has also been declining slightly in the overall population, but it has been increasing slightly in younger adults.

In fact, colon cancer is the leading cause of cancer-related death in adults ages 20 to 49 in the United States.

Smith said that people born around 1990 have twice the risk of colorectal cancer compared with people born around 1950.

“These risks are continuing to rise and are carried forward as people age, meaning we see more diagnoses of colorectal cancer before and after age 45,” he said.

Medical professionals aren’t certain what is causing the increase in early onset colorectal cancer, but diet, lack of physical activity, and obesity are among the suspected causes.

In addition, there has also been some research indicating that intestinal bacteria may also play a role.

Venook said exposure to this type of bacteria as a child may cause colorectal cancer to develop 20 to 30 years down the road.

“We’re still trying to figure all this out,” he told Healthline.

Medical experts say colorectal cancer is curable if caught in its early stages. In later stages, it can be deadly.

They say that’s why screenings are vital.

Current recommendations call for males and females to start being tested for colorectal cancer at age 45.

In addition, screenings may be required before age 45 if a person has a family history of colorectal cancer or has certain medical conditions such as inflammatory bowel disease (IBD).

It’s recommended that colonoscopy screenings be done every 10 years for people with no family history of the disease and no polyps discovered during the exam. The time between tests can be shorter for other patients.

Besides rectal bleeding, other symptoms of colorectal cancer include:

• change in bowel habits
• diarrhea
• constipation
• cramping or abdominal pain
• unexplained weight loss

Smith adds that family history should not be ignored.

“Individuals should know their family history of cancer and any diagnosis of colorectal cancer among family members should be discussed with their doctor, especially if family members were diagnosed at a young age,” he said.