The vast majority of women ages 50 to 74 should consider getting mammograms every three years, instead of every two years as currently recommended, to reduce the potential harms from breast cancer screening, a UW-Madison study says.
More than 80 percent of women that age have a low or average risk for breast cancer and/or have low-density breasts, in which mammograms are likely to detect cancer if present, the researchers said.
By getting screened every three years instead of every two years, such women can avoid many false positives, unnecessary biopsies and other complications, although they would face a slightly higher, but still low, risk of death.
“If they’re lower-risk (for breast cancer), they have a much greater chance of experiencing these false alarms than they will at getting a benefit from mammography,” said Amy Trentham-Dietz, a cancer epidemiologist at the UW Carbone Cancer Center.
Women ages 50 to 74 with a high risk for breast cancer and dense breasts, who make up less than 1 percent of women that age, should consider getting screened every year, according to the study, published Tuesday in the journal Annals of Internal Medicine. One reason is that dense breasts, which have less fatty tissue and more glandular tissue than average, make detection of cancer more difficult.
The remaining women — about 18 percent of those age 50 and 13 percent of women age 65 — may be best off staying with mammograms every two years, the study said.
“Tailored screening is really the goal, to make the balance of benefits and harms the best it can be,” Trentham-Dietz said.
The study “provides evidence so that women and providers can weigh the benefits of screening with their personal risk and preferences,” she said.
The U.S. Preventive Services Task Force says women ages 50 to 74 should get mammograms every two years. The American Cancer Society says women should start annual testing at age 45 and switch to every two years at 55.
The new study, led by Trentham-Dietz, included researchers from Dartmouth College, Georgetown University, Harvard University and the University of California, San Francisco.
The findings should help women and their doctors decide how often each woman needs a mammogram, Dr. Christine Berg, at Johns Hopkins Medicine, wrote in an editorial accompanying the study.
“Their results provide information that the informed patient and clinician can use in making individualized decisions,” Berg said.
In the study, the researchers from the Breast Cancer Surveillance Consortium and the Cancer Intervention and Surveillance Modeling Network used computer models of breast cancer study data and statistics to analyze the harms and benefits of different intervals of mammograms.
They divided women based on the density of their breasts and on risk factors, such as not having children or having children at a later age (which carries a slightly higher risk of breast cancer) and abnormal tissue previously found in the breast (a substantially higher risk).
Women can use an online calculator, go.madison.com/bcsc, to help determine their risk. Breast density is best determined by a mammogram.
Women with average risk of breast cancer and low-density breasts, which make up 12 percent of 50-year-olds and 20 percent of 65-year-olds, should consider screening every three years, the study said.
Women at lower risk, which account for 70 percent of women age 50 and 66 percent of those age 65, also should consider triennial screening, the study said.
That means 82 percent of women age 50 and 86 percent of women age 65 should consider screening every three years and discuss the matter with their doctors, Trentham-Dietz said.
The study didn’t evaluate MRIs, which are generally used for the highest-risk women, including those with certain genetic mutations linked to breast cancer. It also didn’t look at women in their 40s, for which there is considerable debate over whether or how often they should be screened.
Trentham-Dietz said the researchers plan to write another paper about women in their 40s.
[Editor's note: This story has been updated to reflect a correction. The original incorrectly characterized the group of women the study recommends be screened for breast cancer every year. The study suggests women ages 50 to 74 with a high risk for breast cancer and dense breasts, who make up less than 1 percent of women that age, should consider getting screened every year.]