Screening mammography in women under age 40 results in high rates of callbacks, low rates of cancer detection, and high rates of false-positive results, according to the results of a study published early online in the Journal of the National Cancer Institute.
Screening mammography refers to mammograms that are conducted in the absence of breast symptoms. The goal of screening mammography is to detect breast cancer at an early stage when it is most easily treated.
The performance of screening mammography is known to vary by age. Younger women are less likely than older women to have breast cancer, and more likely to experience some of downsides of screening such as false-positive test results. This has made it challenging to identify the optimal age at which screening should begin. The U.S. Preventive Services Task Force recommends that routine screening of average-risk women begin at age 50. The American Cancer Society recommends that screening begin at age 40.
Although a great deal of attention has focused on the performance of screening mammography among women over the age of 40, there has been little information available about how mammography performs in very young women—those under the age of 40. To address this question, researchers from the University of North Carolina pooled data from six mammography registries in the United States. Their data included 117,738 women who underwent their first mammogram between the ages of 18 and 39. The researchers then followed the women for a year to determine the accuracy of the tests, evaluate the recall rate, and measure the cancer detection rates. The study included women who had screening mammograms as well as those who underwent diagnostic mammograms (due to a symptom such as a lump).
The researchers found that mammography performance improved in the presence of a breast lump – for diagnostic mammograms, the rate of detection was 14.3 cancers per 1,000 women tested, whereas for screening mammograms, the rate of detection was 1.6 cancers per 1,000 women. The researchers found that the screening mammograms had poor accuracy and high rates of recall for further testing.
The authors concluded that “in a theoretical population of 10,000 women aged 35-39 years, 1,266 women who are screened will receive further workup, with 16 cancers detected and 1,250 women receiving a false-positive result.” They found no cancers in women under the age of 25 and a poor performance of screening mammography in women ages 35-39.
It should be noted that the researchers did not have complete family history information or information about BRCA1 or BRCA2 mutation status, and were therefore not able to fully assess mammography performance in the subset of young women at high risk of breast cancer.
Women who have questions about when to begin breast cancer screening are advised to talk with their doctor.
 Yankaskas BC, Haneuse S, Kapp JM, et al. Performance of first mammography examination in women younger than 40 years. Journal of the National Cancer Institute. Published early online: May 3, 2010.