Early-onset cancer is the diagnosis given to adults under 50 who develop cancer. Increased incidence has been documented for more than a dozen types, including cancers of the breast, bowel, lung, ovaries and pancreas.
Bowel cancer, the third-most-common cancer type worldwide, has seen particularly steep increases among the young. Compared with Americans born around 1950, those born around 1990 are projected to be twice as likely to develop colon cancer by the age of 50, and four times as likely to develop rectal cancer. The trend appears to be worsening with each successive generation. Similar patterns have been reported in at least 27 countries. Observational studies linking bowel cancer to obesity, alcohol intake and low physical activity have not uncovered anything unique to early-onset cases.
A study published in Nature on April 23rd 2025, led by an international collaboration based at the University of California, San Diego, analysed the genomes of 981 colorectal-cancer tumours from 11 countries. The researchers identified colibactin—a toxin released by several bacteria, including a widespread strain of Escherichia coli—as a likely contributor to premature bowel cancer. Colibactin's mutational signature was present in more than 50% of tumours from patients younger than 40, but fewer than 20% of those above 60. The mutations typically arose in the first ten years after birth, in the specific gene whose impairment triggers bowel cancer.
Stool samples from children in about 20 countries showed that those from countries with higher rates of early-onset cancer were more likely to carry the colibactin-producing strain of E. coli. About a third of healthy adults carry such bacteria, but only a small fraction develop cancer. Rising rates of antibiotic use and caesarean births may disrupt children's microbiomes enough to allow the strain to take root. Some researchers also worry about probiotics that contain the bacterium.
An animal study published in March 2025 in Nature Microbiology found that colibactin-producing E. coli thrived in mice fed a diet low in carbohydrates and soluble fibre. The lack of fibre weakened the protective mucous barrier of the colon, exposing cells to colibactin. A 2022 study led by Shuji Ogino at Harvard found that closer adherence to a Western-style diet was associated with colorectal tumours containing greater amounts of colibactin-producing E. coli.
Three main pathways are being explored: drugs that inhibit E. coli's effects; probiotics that help beneficial bacteria outcompete it; and bespoke bacteria-infecting viruses known as phages. Such research has so far been conducted only in cell cultures or lab animals. The researchers hope to develop stool tests capable of spotting colibactin-induced mutations within five years, which could enable earlier monitoring and intervention.
Strangelove Reproduction: Having children to make up for the fact that one no longer believes in the future.