A new study tracking more than 140,000 women age 66 and older found that getting a mammogram every two years was just as effective as an annual screening in catching cancerous tumors early. Biennial testing did not increase the likelihood that the women would have late-stage cancer if or when the disease was detected. The less-frequent screening also produced far fewer false positive results that can lead to stress, expensive follow-up testing and painful, unnecessary treatment.
Our study shows that it really does very little benefit in fact, there is no benefit with annual mammograms, and there's this additional harm of having an increased probability of a false positive result," Dejana Braithwaite, an assistant professor of epidemiology and biostatistics at the University of California San Francisco and lead author of the study, told Reuters. (The study appeared this week in the Journal of the National Cancer Institute.) The results were consistent across the group studied, even among those who had conditions such as heart disease and diabetes.
The study analyzed data collected from 1999 to 2006 for about 3,000 women age 66 to 74 who developed breast cancer and about 138,000 who didn't, comprising what Braithwaite called "the largest available screening mammography data set in the United States."
The researchers found that 48 percent of the older women who were screened each year had false positive results, as opposed to 29 percent of those who had mammograms every other year. A false positive occurs when a radiologist detects a lesion that appears to be malignant but is later determined not to be after testing such as an ultrasound or biopsy.
Women aged 66 to 74 years who choose to undergo screening mammography," wrote study co-author Karla Kerlikowske, a professor of medicine at UCSF, get no added benefit from annual screening and face almost twice the false positives and biopsy recommendations, which may cause anxiety and inconvenience.
The Larger Mammography Debate Continues
The UCSF findings represent the latest salvo in an ongoing dispute over the most effective recommendations for mammography. The American Cancer Society has long maintained that most women 40 and older should be screened annually. But since 2009, the U.S. Preventive Services Task Force, an independent group of experts supported by the federal Agency for Healthcare Research and Quality, has advised against routine annual mammograms for most women in their 40s. The panel believes the risks of false positives outweigh the benefits for women under 50 because such results can cause anxiety and lead to invasive follow-up tests as well as overtreatment of small tumors that may never have become invasive. Instead, the task force suggests, those women should talk to their doctors about their family history and risk factors to make a determination about how frequently they should be screened.
The panel recommends that women age 50 to 74 have only biennial screenings, and has concluded that there is too little evidence of benefits to make a definitive recommendation on mammogram frequency for women 75 and older.
The cancer society has taken issue with the panel's conclusions, as have some independent researchers. A study presented last fall at the annual Radiological Society of North America conference found that the panel's advice, which has been widely adopted by doctors, hospitals and insurers, may be causing physicians to miss many cases of cancer. That research, from New York-Presbyterian/Weill Cornell Medical Center, found that 4.7 cancers were detected for every 1,000 mammograms at the hospital, but the rate of detection for women in their 40s was only 2.7 cases per 1,000, an indication that as many as 20 percent of potential breast-cancer cases were not being identified because of more limited screening of women in their 40s.
The New York-Presbyterian study did not measure patient outcomes, though, so it could not prove that more frequent screening of women in their 40s would lead to a reduced death rate from breast cancer.
Some experts who have reviewed the UCSF study say it makes a strong case for limited screening in older women, but the debate over the benefits of more widespread annual screening for younger women is likely to continue. According to research by the U.S. National Cancer Institute, the average 40-year-old woman has a 1-in-69 chance of developing breast cancer sometime in the next 10 years; a 60-year-old woman has a 1-in-29 chance.