Recent findings have revealed that young adults who experienced rectal bleeding faced an 8.5-fold higher risk of developing colorectal cancer (CRC) compared to those without the symptom.
A study presented at the American College of Surgeons Clinical Congress 2025 said that young adults experiencing rectal bleeding have a significantly elevated risk of developing colorectal cancer, underscoring the need to take the symptom seriously even in the absence of a family history of colorectal cancer.
Colorectal cancer is also known as bowel cancer. Common causes of the disease include an unbalanced diet featuring too much processed meat, alcohol, and smoking, with little fibre and physical activity. Being overweight and obese contributes to around 11% of cases in the UK.
The retrospective study analysed 443 patients under 50 who underwent a colonoscopy at the University of Louisville Health System between 2021 and 2023. Of them, 195 (44%) were diagnosed with early-onset colorectal cancer, while 248 (56%) had normal results.
The study aimed to help doctors determine which young patients with symptoms should get a diagnostic colonoscopy and found that most (88%) of those later diagnosed with early-onset colorectal cancer had symptoms like bleeding, while just over half (55%) of those without cancer had similar symptoms.
Only 13% of early-onset colorectal cancer cases had a marker often associated with hereditary syndromes, such as genetic alterations that occur in some colorectal cancers.
Patients diagnosed with early-onset colorectal cancer were also significantly more likely to be former smokers (almost two times higher odds).
Senior author Sandra Kavalukas, MD, FACS, a colorectal surgeon at the University of Louisville School of Medicine in Louisville, Kentucky, noted that many early-onset colorectal cancers seen have no family history.
Dr Kavalukas said, ‘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.
‘If they’re 35 and they come in with rectal pain, they probably don’t need a colonoscopy. But if they come in with a bleeding complaint, they are 8.5 times more likely to have colorectal cancer.’
The findings address a critical gap in care for young adults, who are not eligible for routine screening but are experiencing the fastest-rising rates of colorectal cancer. The study provides data to support coverage for diagnostic colonoscopies in symptomatic young patients.
During a colonoscopy, a doctor will inspect your entire large intestine (colon) and rectum while you are sedated to determine the cause of the rectal bleeding.
It can help to find cancer early when it’s easiest to treat – or even to find and remove polyps before they turn into cancer.
Blood can show up in your stool in a variety of ways, and what that blood looks like can give clues as to where it’s coming from. Bright red blood may be a sign of something low in the colon or rectum, such as diverticulosis or haemorrhoids.
Darker blood may be from something higher up. If the blood is black or tar-like, that could signal an issue with the small intestine or stomach. Slowly bleeding tumours at the beginning of the colon, on the other hand, may cause dark red or black stools.
The US Preventive Services Task Force guidelines recommend screening colonoscopies starting at age 45 for most people without a family history of the disease.
The research team is now working on a larger analysis to create a risk score calculator.