"We found a very small increase in the probability of having a late-stage breast cancer for women screened every two years, but this was not statistically significant," she says, meaning it may have been due to chance alone.

A suspicious mammogram which prompts further testing may be scary, but Miglioretti stresses that the vast majority of women who are called back for more imaging or even a biopsy do not have breast cancer.

She adds that one way to reduce the chance of a false-positive result is to have a baseline mammogram so the doctor can see any changes.

"One thing that we found that's important for women to know is that having comparison films available when the radiologist interprets your mammogram greatly reduced the probability of having a false-positive result."

Diana Miglioretti and her colleagues published their study in the Annals of Internal Medicine.

In a separate study in the same issue of that journal, researchers compared digital mammography with traditional film. Overall, the two produced comparable results, but for women in their 40s, digital screening may give better results.

However, the digital scans also produce more false positives, and an editorial in the journal by Philippe Autier, MD, of the International Prevention Research Institute in France suggests that widespread adoption of digital mammograms may reduce the efficiency of breast cancer screening.