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After more than two decades of decline, colorectal cancer rates in the U.S. are rising again — and the increase is spreading beyond younger adults. A new study in NEJM Evidence found rates climbing across nearly every age group under 70, with researchers pointing to a "birth cohort effect" as a likely driver. Scientists are now racing to identify the unknown risk factors behind the troubling reversal.
After more than 20 years of falling rates, colorectal cancer is making an unwelcome comeback in the United States — and it's no longer just a young person's problem. A new study published in NEJM Evidence found that after hitting a low of 36.7 cases per 100,000 people in 2022, the age-adjusted incidence rate climbed back up to 38.3 in 2023. Researchers say rates are now rising across nearly every age group under 70, including older Americans who have historically benefited most from screening.
Scientists attribute part of the trend to a "birth cohort effect" — the idea that people born in the 1960s and later share elevated risk patterns that become more visible as they age. The sharpest single-group jump was among adults 45–49, where incidence rose 12.76% annually from 2019–2023, partly explained by the lowered screening age recommendation from 50 to 45. But rising rates among well-screened older adults suggest unknown risk factors — possibly environmental chemical exposures — are also at play.
By the Numbers
Why it matters: Colorectal cancer is already the #2 cause of U.S. cancer deaths and the #1 cancer killer in adults under 50. If this trend continues as younger birth cohorts age, the healthcare system could face a significant surge in diagnoses and treatment demand — making early screening and urgent research into root causes more critical than ever.
