The October 20, 2015, JAMA article presenting the American Cancer Society’s 2015 Guideline Update for breast cancer screening has been the topic of much media coverage. These guidelines apply to all but those women at very high risk of developing breast cancer — known deleterious mutation carriers, and those with a personal history of breast cancer or a history of previous radiotherapy to the chest at a young age. Modifications of the guidelines appropriate for women at intermediate risk are under development by the American Cancer Society.

The article has reinvigorated a worthwhile discussion about when women should be screened for breast cancer. First, do no harm — this principle of medical ethics must be kept in the forefront of our minds when we contemplate screening programs, which by definition invite people who don’t have symptoms to take part in an intervention. Any screening program involves some harm and some benefit. The risk/benefit ratio is improved if the screening focuses on people who are at higher risk of developing the disease.

“Risk-based screening has the potential to save more lives than our current practice,” said Dr. Otis Brawley, Chief Medical Officer of the American Cancer Society, in an editorial in the Annals of Internal Medicine. “In the future, more emphasis will be placed on risk-based screening guidelines tailored to the individual. There may be recommendations that some women at very high risk get annual testing, some at intermediate risk get biennial testing, and some at normal risk start at a later age.” Dr. Brawley wrote that in 2012, about the time that the Cancer Society began the exhaustive evidence investigation which resulted in the 2015 Guidelines.

The American Cancer Society now recommends that mammography screening for breast cancer should start at age 45. It is true that the incidence of breast cancer increases with age, and that screening only after 45 is selecting individuals at slightly higher risk than women under 45, but there are also several other risk factors for breast cancer.

Mammographic breast density is emerging as a significant risk factor. Women of any age who have a totally fatty density breast on mammography have a very low risk of developing breast cancer. Conversely, women with extremely dense breasts (about 8 percent of women over 40) have a twofold increase in risk of breast cancer. Having a first-degree relative (a parent, child or sibling) diagnosed with breast cancer before age 40 is associated with a threefold increased risk of breast cancer, and having two first-degree relatives diagnosed with breast cancer is associated with almost a fourfold increase in risk.

The guidelines, by intention, leave a lot of room for individualization. My strong suggestion is that each woman, in consultation with her primary care physician, use risk factors such as extremely dense breast tissue, first-degree relatives with breast cancer and personal history of breast biopsies to decide whether to start screening at 40 vs. 45, and whether to have annual or biennial screening after age 55.

A mammography screening program based on more risk factors than just age might look like this:

A woman might have a screening mammogram at age 40. If the breast is fatty density or scattered fibroglandular density, and if the woman has no previous breast biopsies and no family history of breast cancer, she need not have another mammogram until age 45. A woman at 45 should begin routine annual mammographic screening. If the woman over 55 has fatty breast density or scattered fibroglandular elements, and no significant breast cancer risk factors, she may safely be tested every two years. These recommendations, based on very large, well done recent studies based on data from the Breast Cancer Surveillance Consortium, are very similar to the evidence-based recommendations published in 2009 by the United States Preventive Services Task Force.

Mammography does save lives. It is responsible for about a 15–30 percent decrease in mortality from breast cancer. We just need to tweak our protocols a little bit to get the most benefit with the fewest false positive results and the fewest other harms.