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Colorectal cancer cases are increasing across nearly all age groups under 70 in the United States, reversing more than two decades of declining rates and raising concerns about a growing public health challenge, according to a new study published in NEJM Evidence.
The findings suggest that the increase is no longer limited to younger adults, who have experienced a steady rise in diagnoses in recent years. Researchers warn that the trend could place additional pressure on the healthcare system as more people require cancer treatment and long-term care.
A research team led by Caitlin Murphy, a professor of pediatrics and public health sciences at the University of Chicago, analysed colorectal cancer incidence data from the US National Cancer Institute covering the period from 2000 to 2023.
The study found that the age-adjusted incidence rate fell from 55.2 cases per 100,000 people in 2000 to 36.7 in 2022. However, it rose to 38.3 in 2023, marking the first overall increase in more than 20 years.
Researchers also found that cancer rates were rising across every age group up to 65-69 years, indicating that the trend is spreading beyond younger generations.
Murphy said the findings could be linked to a phenomenon known as the “birth cohort effect”, in which people born during similar periods share risk factors that become more evident as they grow older.
She suggested that generations born during the 1960s and later may be carrying an elevated risk of colorectal cancer into middle age and beyond.
One of the sharpest increases was recorded among people aged 45 to 49. Colorectal cancer incidence in this group rose by an average of 12.76 per cent annually between 2019 and 2023.
Researchers said the increase was partly associated with changes in screening guidelines. The recommended starting age for routine colorectal cancer screening in the US was lowered from 50 to 45, resulting in more people being tested and previously undetected cancers being identified.
However, expanded screening does not fully explain the broader rise. Incidence has also increased among adults aged 65 to 69, while the previous decline has stalled among those aged 70 to 74.
Around 80 per cent of people in these older age groups are up to date with recommended screening, suggesting that other risk factors may be contributing to the increase despite widespread testing.
The researchers also examined whether the COVID-19 pandemic had affected the findings by disrupting cancer screening and diagnosis. However, the upward trend remained even after data from 2020 and 2021 were excluded.
Sonia Kupfer, director of the Gastrointestinal Cancer Risk and Prevention Clinic at UChicago Medicine, said the findings highlighted the need to identify the causes of the increase so that risk factors could potentially be reduced.
Colorectal cancer is the second leading cause of cancer-related deaths in the United States and the leading cause of cancer deaths among adults under 50.
Data from the American Cancer Society show that incidence among people aged 20 to 49 increased by approximately 3 per cent annually between 2013 and 2022.
Researchers say understanding why the disease is becoming more common among younger adults could also help explain the rising rates among older generations and guide future prevention strategies.
