Colorectal cancer becomes top cancer killer in adults under 50, researchers warn

Colorectal cancer has overtaken other cancers to become the leading cause of cancer death among Americans under 50, according to new data published this week. The alarming shift underscores a years-long trend that has puzzled oncologists and spurred urgent research into what is driving the disease in younger populations.

Rising rates in young adults

While colorectal cancer rates have declined in older adults thanks to improved screening, incidence in people under 50 has been climbing by roughly 2% annually since the 1990s. The disease is now the fourth-most diagnosed cancer in this age group but the deadliest. Researchers say the trend is not limited to the United States — similar patterns are emerging in Canada, Australia, and parts of Europe, suggesting a global shift in risk factors.

Warning signs often missed

Younger patients are more likely to be diagnosed at advanced stages, in part because early symptoms are frequently dismissed or misattributed to hemorrhoids, irritable bowel syndrome, or dietary issues. Medical organizations are pushing for greater awareness of warning signs: persistent changes in bowel habits, rectal bleeding, dark or narrow stools, abdominal pain, and unexplained weight loss. Anyone experiencing these symptoms for more than two weeks should seek evaluation regardless of age.

What's driving the trend?

The exact causes remain unclear, but researchers point to several suspects: rising rates of obesity, sedentary lifestyles, diets high in processed foods and low in fiber, and changes in the gut microbiome. Some studies have also linked early-life antibiotic use and exposure to certain environmental chemicals to higher colorectal cancer risk. The American Cancer Society recommends screening begin at age 45, but experts say the data make a case for even earlier screening in high-risk populations.