The downside of mammograms

A 17-year study has concluded that screening mammography — in which all women in certain age groups are routinely screened for breast cancer — does not reduce the incidence of advanced tumours but does increase the diagnosis of lesions that would never have led to health problems.

In Denmark, screening was implemented in different regions at different times, so researchers there were able to compare groups of women who were screened for breast cancer with those who were not.

If screening were effective, a reduction in the incidence of advanced tumours would be expected — tumours would be caught and treated when small. Instead, the researchers found no difference in incidence between screened and unscreened groups.

But in screened groups, they found substantial overdiagnosis — that is, detection of tumours that would not become cancers needing treatment.

The study, published in the journal Annals of Internal Medicine, found that, depending on age and other factors, between one-fifth and one-third of tumours detected by screening were overdiagnosed. The researchers concluded that screening does not prevent advanced cancers or lower breast cancer mortality.

“Some types of screening are a good idea — colorectal, for example,” said lead author Dr Karsten Juhl Jorgensen, deputy director of the Nordic Cochrane Center.

“But breast cancer has a biology that doesn’t lend itself to screening. Healthy women get a breast cancer diagnosis, and this has serious psychological consequences and well-known physical harms from unnecessary treatment. We’re really doing more harm than good.”