Ohio oncologist Ning Jin has observed an increasing number of late-stage lower digestive tract cancer cases among patients in their 30s and 40s. Tumors in younger colorectal cancer patients are more resistant to treatment than those typically seen in older patients, according to Jin.

"Even though we treat young patients with more aggressive chemo — more chemo or more surgery — patients' outcomes are not necessarily better," Jin said. Earlier-onset colorectal tumors are more often located near the rectum, in the lower part of the digestive tract.

Colorectal cancer has become the leading cause of cancer death among people under 50, while death rates for colorectal cancer have declined in older age groups. Recent scientific advances have made many cancers more treatable and survivable, but colorectal cancer has become more lethal and more frequent among younger patients. Preventive colorectal cancer screening is not routinely recommended or covered by insurance until age 45.

The shift has reshaped clinical practice over a generation. "Thirty-plus years ago, when I first started, no one — no one; zero number of patients — were in my clinic under the age of 50 with colon cancer. And now it is almost half of the patients that I see," said John Marshall, head of clinical research at the Lombardi Cancer Center at Georgetown University.

A study found an association between the DNA-damaging toxin colibactin, produced by certain E. coli strains, and colon cancer in younger patients. Marshall notes that different parts of the digestive tract — mouth, stomach, and gut — have distinct chemistries and microbiome compositions that may contribute to tumor formation. "We don't know how to test it, we don't know how to make a good one," Marshall said regarding microbiome health assessment.

Jin says that exposure to chemicals in laundry detergents and processed foods may disrupt the gut's protective mucus layer, leading to inflammation and increased intestinal permeability. Up to one in five colorectal cancer patients have hereditary genetic markers, such as a Lynch syndrome mutation, that increase cancer risk, though genetic factors do not account for about 80% of colorectal cancer cases.