Colorectal cancer: US incidence is rising again
· BehindLines newsroom
After more than twenty years of decline, the overall rate of colorectal cancer has risen in the United States, as shown by a study in NEJM Evidence. The work, carried out at the University of Chicago, is presented by UChicago Medicine; ScienceDaily carries the same content and therefore provides no independent source. The findings indicate that the increase is no longer limited to young adults.
A curve that reverses
The team of Caitlin Murphy, an epidemiologist who teaches pediatrics and public health sciences, analysed National Cancer Institute incidence data for 2000 to 2023. The age-adjusted rate fell from 55.2 cases per 100,000 people in 2000 to 36.7 by 2022, before climbing to 38.3 in 2023. "For the first time in over two decades, we are seeing the overall rate go up," says Caitlin Murphy. According to the study, rates are rising in every age group up to 65-69.
Screening, cohort effect and unknowns
The sharpest rise concerns people aged 45-49, with +12.76% per year between 2019 and 2023. According to the authors, it is probably due to the lowering of the recommended screening start age, from 50 to 45: more people are tested, so more cancers are found. This explanation does not hold, however, for people aged 65-69, where incidence is rising, nor for those aged 70-74, where the decline has stalled. About 80% of people at these ages are up to date with screening, which suggests that risk factors not yet identified may be cancelling out part of what screening has achieved.
Murphy speaks of a "cohort effect": people born from the 1960s onwards would face a higher risk as they reach middle age. The researchers also removed 2020 and 2021 from the analysis to test the effect of the Covid-19 pandemic; the increase persists.
Causes still to be established
The researchers cannot yet say which factors are involved. The team is looking at exposure to environmental chemicals, with toxicologist Xin Hu of Emory University. It plans to measure thousands of exposures in a small blood sample, in order to pick out the substances worth investigating further, then study their effects on colon organoids, models grown in the laboratory. This is therefore a line of research, not a result.
Why it matters
This study describes US statistical trends drawn from a registry; it does not demonstrate any cause. According to Caitlin Murphy, if these trends continue, the rise in diagnoses in a large and ageing population could place a heavy burden on the health system for treatment and follow-up. The authors ask for monitoring to continue, since the registry data are updated every year.