WHILE most older women might not need breast cancer screening with mammography more often than every three years, some women with dense breasts may need mammograms every year, US research suggests.

Among women aged 50 to 74, those without a high risk for breast cancer or dense breast tissue didn't have an increase in breast cancer deaths if they went for mammography every three years instead of every two years.

But with dense breasts and a higher risk for these tumours, yearly mammograms were associated with fewer breast cancer deaths than screening every other year, researchers report in the Annals of Internal Medicine.

“Women at low risk and low breast density will experience more harms with little added benefit with annual and biennial screening compared to triennial screening, whereas women with dense breasts and high breast cancer risk may have added benefit from annual compared to biennial mammography,” lead study author Amy Trentham-Dietz of the University of Wisconsin-Madison said.

Doctors are conflicted about when and how often to recommend routine screening mammograms for women who don't have lumps or discomfort in their breasts.

Last year, the American Cancer Society shifted its guidelines to encourage women to start annual screenings at 45 instead of 40 and to cut back to every other year once they turn 55. The US Preventive Services Task Force recommends mammograms every other year for women ages 50 to 74.

Worldwide, breast cancer is the most common malignancy in women. About one in nine women will eventually develop it and the risk increases with age, and when a woman's mother, sister or daughter has been diagnosed with the disease. Compared with screening every two years, getting mammograms every three years could reduce false positives, biopsies and over-diagnosis without much effect on the number of cancer deaths averted for the majority of women – the ones with average cancer risk and lower breast density.

When women had a high risk of breast cancer, however, annual screening was better regardless of breast density, noted Dr Christine Berg of Johns Hopkins University School of Medicine in Baltimore, who wrote an accompanying editorial.

The way women know if they have dense breasts is to get a mammogram and density can change over time, noted Dr Pamela DiPiro of the Dana Farber Cancer Institute in Boston.

“Annual mammography is a patient's best chance of detecting breast cancer early with the known caveat that additional imaging, ultrasound or even a benign biopsy may be recommended,” said DiPiro, who wasn't involved in the study.

Still, the take-home message for women is complicated, said Dr Kathryn Evers, director of mammography at Fox Chase Cancer Centre in Philadelphia.

“There are no definitive answers – women should talk to their doctors about what regimen will be best for them, taking all of these factors into account,” Evers added.