Jeremy Laurance: Too much information can be bad

Being told you have a life-threatening condition is no joke. The disease may be harmful, but so can the knowledge that you have it.

This is not widely understood by patients. There is an assumption that, if you have cancer, the sooner you know about it, the sooner you can do something about it and the better your chance of a cure.

While this is true, it is not always so. In some cases – one in three according to the latest study – the cancer detected in screening does not need treating, either because it resolves naturally or because it is very slow growing (so you die of something else).

In these cases, the only result of screening is that you spend more of your life living in the shadow of cancer, without living longer. You may be treated, and suffer pain and anxiety, to no avail. That is not just of no benefit – it is grim.

This is a problem for all screening programmes. In some cases, as with prostate screening, the problem of "overdiagnosis" is so great that routine screening is regarded as unwise (at least in the UK). In breast screening, overdiagnosis is a lesser problem so it is worthwhile offering it to women.

Ultimately, however, this is a matter that each woman can only decide for herself, having assessed the benefits and harms.