A new study released in the journal Cancer reconsiders guidelines for when to start screening with mammograms if a woman has a mother, sister, or daughter who was diagnosed with breast cancer.

Women with a first-degree family relative diagnosed with breast cancer, who are otherwise at average risk, are often advised to get screened 10 years earlier than the relative's diagnosis age. However, there is little evidence to support the long-standing recommendation.

UC Davis Comprehensive Cancer Center researcher Diana Miglioretti joined Danielle Durham, with the Department of Radiology at University of North Carolina at Chapel Hill, and five other researchers on the study. They analyzed data from the Breast Cancer Surveillance Consortium on screening mammograms conducted from 1996-2016 to evaluate when screenings should begin for women with a family history of breast cancer.

More than 300,000 women were included in the national study. Researchers compared cumulative 5-year breast cancer incidence among women with and without a first-degree family history of breast cancer by relative's age at diagnosis and screening age.

"The study concluded that a woman with a relative diagnosed at or before age 45 may wish to consider, in consultation with her doctor, initiating screening 5-8 years earlier than their relative's diagnosis age, rather than a decade earlier. That puts them at a risk that is equal to that of an average-risk woman who is age 50, which is the most recommended age for starting mammograms," said Durham.

BRCA gene mutation carriers may benefit from starting screenings earlier. Women ages 30-39 with more than one first-degree relative diagnosed with breast cancer may wish to consider genetic counseling.

Increasing the age for initiating screening could reduce the potential harms of starting breast cancer screenings too early. These include increased radiation exposure and false positive results that require women to return to the clinic for diagnostic imaging and possibly invasive procedures, but do not result in a breast cancer diagnosis. The earlier a woman starts receiving mammograms, the more screenings they will undergo over their lifetime—and that increases the chances of experiencing these harms.

"Mammography also may not perform as well in younger women because they are more likely to have dense breasts which increase the difficulty of finding cancer on the images and results in more false-positives," Miglioretti said.