For nearly 14 years researchers have been gathering information regarding the efficacy of annual versus biennial mammograms.
Now, after collecting data on almost a million women - 11,474 with breast cancer and 922,624 without - a team led by Dr. Karla Kerlikowske of the University of California-San Fransisco School of Medicine has published the results in JAMA Internal Medicine.
The verdict: women between the ages 50 and 74 who undergo a mammogram every two years are just as likely to catch a tumor before it reaches advanced stages as women of the same age who are checked annually. This was true even for those with dense breast tissue and women who had received hormone therapy.
What's more, they are less likely to experience a false-positive diagnosis, which has been shown to cause significant mental injury even years after the event. This is especially relevant given that more than half of abnormal mammograms are wrongly diagnosed as cancerous, according to a study published in the journal Annals of Family Medicine.
For women between the ages of 40 and 49 with extremely dense breasts, however, researchers found a different story.
Women in their forties who only underwent the examination on a two-year basis were nearly twice as likely to be diagnosed with advanced-stage cancer and more than twice as likely to be diagnosed with large tumors when compared with women of the same age who received a mammogram on a yearly basis.
However, once again these women, those receiving a mammogram biennially, were less likely to receive false-positive diagnoses. As before, this was especially true for those with dense breast tissue and those who had undergone hormone therapy.
For this reason, Kerlikowske writes that women who fit this category - that of 40 to 49 years old with extremely dense breasts - should be informed that an "annual mammography may minimize their risk of advanced-stage disease but the cumulative risk of false-positive results is high."