(Reuters Health) - 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, U.S. research suggests.

A woman undergoes a mammography exam, a special type of X-ray of the breasts used to detect tumours, as part of a regular cancer prevention medical check-up at a radiology center in Nice, November 5, 2012. REUTERS/Eric Gaillard

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 tumors, 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 by email.

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. Even though these exams can save lives, they can sometimes subject women to unnecessary and painful treatments that don’t find tumors or lower their risk of dying from cancer.

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 U.S. 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.

Typically, if there is a suspicious area on a mammogram, women get additional imaging to rule out cancer, followed by a biopsy if more information is still needed to determine if the suspect cells are malignant. When the extra tests don’t find cancer, the mammogram result is considered a “false positive.”

For the current study, researchers estimated the odds of false positive mammograms, biopsies that didn’t find cancer and deaths averted based on age, cancer risk factors and breast density.

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.

However, “breast cancers are also more difficult to detect in dense breasts,” Berg added by email. “Therefore annual mammograms allow for comparison of subtle changes.”

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,” DiPiro, who wasn’t involved in the study, said by email.

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

“There are numerous risk factors for breast cancer and women have different levels of comfort with the risks and benefits involved,” Evers, who wasn’t involved in the study, said by email.

“The fact that there are so many different recommendations regarding when and how often women should be screened points out that 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.

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