alt Hacker NewsIf you screen more people for the disease, and do it better, such that you reduce the incidences and fatalities in the 50+ cohort, that improvement logically implies that you must be catching incidences in the under 50 cohort. So it's going to skew the numbers. Incidences that would have been tallied in the 50+ cohort, are now counted in the under 50.
E.g. a 45-year-old with a latent colorectal cancer who would previously not have been diagnosed early, but only late when they developed symtpoms, by which time they hit 50, would have counted as an incidence or a likely fatality, among the 50+ data. But if that same individual had been caught at 45, they would have counted as an incidence against int he under-50 cohort.
Earlier, better and more available screening alone will shift the data this way.
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This mostly can't explain the fact that mortality is also rising in under 50s. It is true mortality is rising less than incident, and that a small proportion instances of mortality could be deaths related to reasonable risks taken on from treatment side effects (to make up numbers, it makes sense to take a 5% chance of dying from treatment this year over a 80% chance of dying from cancer in 5 years), but this is probably not the whole effect. Something is causing more CRC in people under 50.