For every two lives saved through breast cancer screening one woman has unnecessary treatment according to new research.

Breast cancer screening saves two lives for each unnecessary treatment. Photograph: Yongjiet

This would come as a shock to people who believe that screening is faultless. Screening programmes do save lives but they also have disadvantages.

Screening detects the onset of a disease which gains an advantage from early treatment. In the case of breast cancer, if detected early it can be treated successfully with less aggressive management.

But to successfully diagnose the early stages of a disease there needs to be an agreed cut off for those who do have the disease and who do not. The people that test positive can then go on to have further investigations and treatment.

The problem is that having an agreed cut off means that there are people either side of the fence. People who test positive that don’t have the disease (false positives) and people who test negative that actually do have the disease (false negatives). Falling into either category can cause problems:

False positives lead to invasive tests, treatment and the associated anxiety of a cancer diagnosis.

False negatives lead to false reassurance, which can cause late presentation of a condition which may have become untreatable.

Obviously given the choice someone would rather have a false positive than a false negative, and so cut offs tend to be waited towards providing more false positives than false negatives.

So what do today’s results mean? Well although it sounds as if the new research is highlighting the disadvantage of breast screening it is actually a welcomed result.

This is because critics had claimed that for every one woman saved, ten underwent unnecessary treatment. Now women can be reassured that the screening is doing more good than harm.

Image: Youngjiet