For many years, colorectal cancer was considered a disease that mainly affected older adults. Doctors often focused screening efforts on people over the age of 50 because the risk was believed to rise later in life.
However, that picture has been changing. Around the world, and especially in developed countries, more young adults are being diagnosed with colorectal cancer than ever before.
This growing trend has concerned doctors and researchers because younger adults often do not qualify for routine screening programs. As a result, cancers may go undetected until symptoms appear and the disease has already progressed.
A recent study highlights one symptom that may be especially important for younger adults and their doctors to take seriously: rectal bleeding.
Colorectal cancer develops in the colon or rectum, which are parts of the large intestine. The disease often begins as small growths called polyps that can slowly develop into cancer over time.
When found early, colorectal cancer is often highly treatable. Unfortunately, many people ignore early warning signs or assume their symptoms are caused by less serious conditions such as hemorrhoids.
The new study examined 443 patients under the age of 50 who underwent colonoscopy procedures at the University of Louisville Health System between 2021 and 2023.
A colonoscopy is a medical test that allows doctors to examine the inside of the colon and rectum using a flexible camera. It is considered one of the most effective tools for detecting colorectal cancer and precancerous growths.
Among the patients included in the study, 195 people, or about 44 percent, were diagnosed with early-onset colorectal cancer. The remaining 248 patients had normal colonoscopy results.
When researchers analyzed the data, one symptom stood out clearly. Patients who reported rectal bleeding before their colonoscopy were much more likely to be diagnosed with colorectal cancer than those who did not have bleeding. In fact, the presence of rectal bleeding increased the likelihood of a colorectal cancer diagnosis by 8.5 times.
This finding is important because many younger adults may dismiss rectal bleeding as a minor problem. Some people may feel embarrassed discussing the symptom with a doctor, while others may assume it is caused by hemorrhoids or other harmless conditions. The study suggests that such assumptions can be risky.
Researchers found that many of the younger patients diagnosed with colorectal cancer did not have traditional risk factors. Family history is often considered one of the strongest predictors of colorectal cancer, but many of these patients had no known family history of the disease.
Dr. Sandra Kavalukas, a colorectal surgeon and one of the study’s authors, explained that she frequently treats younger colorectal cancer patients who have no family history at all.
According to her, the study helps answer an important question that many doctors face: which younger patients should receive a colonoscopy before reaching the standard screening age?
The findings suggest that rectal bleeding should be considered a strong reason to investigate further, regardless of a person’s age. A young adult who experiences rectal bleeding may benefit from a colonoscopy even if they have no known genetic risk factors or family history of cancer.
The study also found that symptoms played a major role in identifying cancer cases. Among patients diagnosed with colorectal cancer, 88 percent had undergone colonoscopy because they were experiencing symptoms. By comparison, only 55 percent of patients without cancer had symptoms that led to testing.
This difference suggests that symptoms can provide valuable clues when deciding who should be evaluated more closely. Rectal bleeding appears to be one of the most important warning signs.
The researchers also looked at inherited genetic risk factors. Interestingly, only 13 percent of the cancer patients carried genetic markers commonly linked to hereditary cancer syndromes. This means that the vast majority of cancers in the study were not explained by inherited genetic conditions.
Although having a family history of colorectal cancer did increase risk, the effect was much smaller than the impact of rectal bleeding. Family history roughly doubled the risk, while bleeding increased the likelihood of cancer by more than eight times.
The study identified another possible risk factor as well. Former smokers were nearly twice as likely to have colorectal cancer compared with people who had never smoked. This finding suggests that lifestyle factors may contribute to the increasing rates of early-onset colorectal cancer, although more research is needed to fully understand the connection.
To help explain the findings, Dr. Kavalukas offered a practical example. If a 35-year-old patient experiences rectal pain but no bleeding, a colonoscopy may not be necessary.
However, if that same patient reports rectal bleeding, the level of concern becomes much higher. In such cases, a colonoscopy may detect cancer early enough to significantly improve treatment outcomes.
Current guidelines from the U.S. Preventive Services Task Force recommend routine colorectal cancer screening beginning at age 45 for people at average risk. However, many younger adults fall outside these recommendations and may not be screened until symptoms develop.
As cases of early-onset colorectal cancer continue to rise, researchers believe symptoms should play a larger role in deciding who needs testing. The team is now conducting a larger study with the goal of creating a simple risk calculator.
This tool could help doctors identify younger patients who would benefit most from colonoscopy based on their symptoms and personal risk factors.
The message from the research is clear. Rectal bleeding should never be ignored, even in younger adults who appear healthy and have no family history of cancer. Paying attention to this symptom and seeking medical advice early could lead to earlier diagnosis, more effective treatment, and potentially save lives.
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