The possibility that a breast cancer tumor might be missed when it’s early enough to save a life alarms most women. But the ground first started to shift under the question of mammogram frequency in 2009, when the general government guidelines changed from screenings every 1 to 2 years for women over 40 to screenings every 2 years beginning at age 50. (Women in their 40s were advised to decide individually, with their doctors.) Medical and advocacy groups lined up on both sides of the 40-to-50 age gap, and the debate continues to this day.“If you want to confuse people, just publish a table of the various medical organizations and what their mammography guidelines are,” says Barbara Monsees, MD, chairwoman of the American College of Radiology Commission on Breast Imaging. “Among the major groups—the American College of Physicians, the American Congress of Obstetricians and Gynecologists, the American Cancer Society—no one agrees.“Why The Shifting Science Matters To YouMammograms have been subjected to plenty of scientific scrutiny: More than 600,000 women have been tracked in 10 randomized clinical trials around the world, and everyone draws on that data.Although that data doesn’t change, what scientists make of it does. “It’s not that people can’t make up their minds,” says Susan Love, MD, chief visionary officer and director of the Dr. Susan Love Research Foundation. “It’s that the science has changed, and so the results get reinterpreted.” Additionally, because the trials vary so much—in terms of ages studied, design, and execution, for example—some researchers don’t consider them all comparable or valid.What’s more, how the data is interpreted depends on who’s doing the interpreting. The 2009 guidelines that overthrew nearly 30 years of practice came from the US Preventive Services Task Force, an independent group of preventive medicine and primary care physicians appointed by the US Department of Health & Human Services. The task force is charged with evaluating existing studies and preventive medical practices and then recommending guidelines. This group’s recommendations carry great weight because they influence which procedures are covered by insurance. But the 2009 guidelines were so controversial that the US government opted not to apply them to Medicare recipients, who still get yearly mammogram coverage starting at age 40. Private insurance policies vary.If both doctors and government bodies are conflicted, how is an ordinary woman supposed to decide?First, you need to understand the two opposing points of view in order to assess which course is right for you. The Case For Getting Mammograms Every 1 to 2 Years, Starting At Age 40"Mammography screening saves lives,” says Daniel Kopans, MD, director of the breast imaging division at Massachusetts General Hospital and an outspoken critic of the task force report of 2009. “The attacks on mammography screening, particularly for women ages 40 to 49, are a major medical scandal.“Advocates say that it’s undeniable that using mammography to find early stage invasive breast cancer can reduce mortality: More than 40% of the years of life lost to breast cancer are among women diagnosed in their 40s. The recommendation to begin mammograms at 50, according to Dr. Kopans, is arbitrary. “There’s no scientific or biological reason to delay screening until age 50,” he says. In addition, although false-positive readings are a concern, not scanning has perils too. A recent Harvard study showed that almost 75% of women who died of breast cancer were among the 25% not getting regular mammograms. “The same computer models that the task force used to arrive at its guidelines also show that if women now in their 30s followed those recommendations, as many as 100,000 would die unnecessarily from breast cancer,” Dr. Kopans says. Who Supports It: The American Cancer Society, the National Cancer Institute, the American College of Radiology, the American College of Obstetricians and Gynecologists, Susan G. Komen for the Cure, and the American Medical Association.The Case For Getting Mammograms Every 2 Years, Starting At Age 50"So far, studies have demonstrated only that you can find cancers,” says Virginia Moyer, MD, MPH, chairwoman of the task force. “You also have to show that people whose cancers were found earlier benefited. Say you find a tumor when someone’s 45 and she lives till age 60. But if you hadn’t found it till she was 52, she would still have lived to 60. All that’s changed is how long she knows that she has cancer.“The task force and its supporters also point to the emotional, financial, and physical costs of false-positives: the follow-up scans and biopsies of suspected tumors that turn out to be merely distortions of a mammography image or benign lumps. Younger women are more likely to get false-positives. A recent study showed that after 10 years of annual scans, 61% of women ages 40 to 49 would get at least one false-positive result.These experts further contend that it’s not clear whether the increase in diagnoses is simply the result of more women being screened. Breast cancer is the most common malignancy in North American and European women, yet mortality in the United States decreased 30% from 1990 to 2005. For some medical analysts, this success rate suggests that too many breast cancers are being diagnosed, and a portion of the cancers being found by mammograms might never be life threatening. About 30% of tumors will likely respond to treatment no matter when found, and 30% may be fatal regardless. But for another 20 to 30% of tumors, early detection and treatment can make a profound difference. That’s the mammogram “sweet spot.” Since mammograms can’t identify which cancers fall into that sweet spot, they’re all treated similarly. Advocates say that diagnosing tumors early without being able to assess their relative threat leads to over-treatment with chemo and radiation, which come with very real dangers of their own. “In the ‘war against cancer,’ there’s a lot of collateral damage,” Dr. Moyer says. “Because of aggressive screening, a lot of people have adverse events or die from unnecessary surgery, chemotherapy, and radiation, and they are being sacrificed for the people who do benefit. It’s unfair.“Who Supports It: The US Preventive Services Task Force, the American Academy of Family Physicians, the American College of Physicians, the National Breast Cancer Coalition, the Dr. Susan Love Research Foundation, and the World Health Organization. MORE: 20 Ways to Prevent Cancer So What Should You Do To Protect Yourself?Here, in the absence of a universal guideline, is Prevention’s strategy for you:1. Think Preventively.You can do a lot to decrease lifestyle risks, says Therese Bevers, MD, medical director of the Cancer Prevention Center at M.D. Anderson Cancer Center in Houston. “Limit alcohol, exercise regularly, and eat a largely plant-based diet.“2. Know Your Risk Factors.Although only one-third of women with breast cancer have known risk factors, those are still some of the best predictors we have for the disease. Some of the most important:

A family history of breast cancer 

A genetic predisposition such as the BRCA1 or BRCA2 mutation 

Dense breasts 

Radiation exposure early in life

For more on evaluating your risk, visit the Breast Cancer Risk Assessment Tool at cancer.gov/bcrisktool.3. Be Alert to Changes In Your Body.Breast self-exam should never substitute for mammography, but it can help you learn what’s normal for you. See 5 Steps of a Breast Self-Exam to learn how to perform one properly.4. Choose a Screening Schedule After a Discussion With Your Doctor.“Your ob/gyn should talk you through the benefits and limitations of mammograms generally and as they relate to you specifically,” says Mary Jane Minkin, MD, clinical professor of obstetrics and gynecology at the Yale School of Medicine and a Prevention advisor who has been practicing medicine for 33 years. You and your doctor should also consider how concerned you are about cancer, false-positives, and finances, she says: “Most likely, she won’t try to talk you into or out of any particular choice, but she’ll want you to decide based on real evidence and information. I personally recommend mammograms every 1 to 2 years starting at age 40, but it’s your decision. Just be sure you’re getting mammograms at least every 2 years after age 50.” MORE: 10 Ways To Stop Breast Cancer