Colorectal cancer is increasingly showing up in younger adults, with cases now appearing in people as young as their thirties — often with no family history or warning signs. A major Swiss study analyzing nearly 100,000 cases over four decades found that diagnoses in people under 50 have been steadily climbing, even as rates fall among older adults thanks to screening programs. Researchers say younger patients are also more likely to be diagnosed late, after the cancer has already spread.