After getting annual mammograms for 10 years, most women in the US have had at least one false positive and seven to nine per cent have been asked to get a biopsy, a US study found.

“We conducted this study to help women know what to expect when they get regular screening mammograms over the course of many years,” explained Rebecca Hubbard, a Group Health Research Institute researcher in Seattle and an author of the research which appeared in the October 17 edition of Annals of Internal Medicine.

“We hope that if women know what to expect with screening, they’ll feel less anxiety if – or when – they are called back for more testing. In the vast majority of cases, this does not mean they have cancer,” Hubbard added.

Having a mammogram every two years would likely reduce the incidence of false positives but also could delay a cancer diagnosis, the researchers found.

Still, for those diagnosed with a cancerous tumour, the authors of the study did not find that women getting an exam every two years had a greater risk of advanced cancer than those getting annual mammograms.

The study looked at some 170,000 women from 40-59 across the US and some 4,500 who were treated for metastisised breast cancer.