Colorectal cancer has become the leading cause of cancer deaths among Americans under age 50, according to a new study published Wednesday (January 22) in the Journal of the American Medical Association. This marks a major shift from three decades ago, when it ranked fifth among cancer deaths for this age group.

The research, conducted by the American Cancer Society, analyzed more than 1.2 million cancer deaths in people younger than 50 from 1990 through 2023. The study found that while the overall death rate from cancer in this age group fell by 44%, deaths from colorectal cancer increased by about 1.1% each year since 2005. This trend stands in sharp contrast to declining death rates for other major cancers, including lung, breast, brain, and leukemia. The findings were reported by the American Cancer Society and confirmed in the JAMA study.

Researchers say the rise in colorectal cancer deaths came sooner than expected. “We weren’t expecting colorectal cancer to rise to this level so quickly, but now it is clear that this can no longer be called an old person’s disease,” said Dr. Ahmedin Jemal, senior vice president at the American Cancer Society, as cited in the ACS report. Experts are not certain why rates are increasing in young people, but theories include higher rates of obesity, less physical activity, changes in diet, and shifts in gut bacteria.

The study also found that three out of four younger patients are diagnosed after the cancer has already advanced, making early detection critical. The U.S. Preventive Services Task Force now recommends that adults at average risk start regular colorectal cancer screening at age 45, and even earlier for those with a family or genetic history.

While researchers investigate the causes behind this rising trend, they urge younger adults to be aware of symptoms—such as blood in the stool or persistent stomach pain—and to take advantage of screening opportunities. “Lives can be saved now through symptom awareness and destigmatization, and more screening uptake,” said Rebecca Siegel, lead author of the study, in the ACS statement.

The American Cancer Society calls for expanded access to preventive care and continued research to understand why colorectal cancer is on the rise in younger Americans. In the meantime, experts stress the importance of early detection to turn back the tide on this worrying trend.