And although there appears to be a lower death rate among cancer patients soon after they have been screened, the rate evens out over the years until there is no difference at all between screened and unscreened cancer patients.
A positive reading can trigger a range of further tests and treatments, which can be fatal, and the cancer patient is more likely to commit suicide or die from heart disease after diagnosis.
In one study of 46,000 people screened for colon cancer, there were 192 deaths per 10,000 in those who were not screened, and 128 deaths in the screened group—but this advantage disappeared over the years until there was the difference of just two deaths between the groups.
Research isn’t picking up the overall survival rates between the two groups because the studies aren’t big or powerful enough to do so, says Vinay Prasad, an oncologist who is a professor at the Oregon Health and Science University.
To really know the true benefits—if any—of screening, researchers would need to set up studies involving more than four million people, and these would cost upwards of $1bn.
Prof Prasad says that patients have an overly-optimistic view of the benefits of cancer screening, while its advocates emphasise those benefits to the point where they could be accused of fear mongering.
Doctors need to be more honest about the limitations of screening, he says.