Mammography is the best tool for detecting breast cancer early. But whether it's a lifesaver for women in their 40s has been debated. This is where the experts stand now.

Over the last few years, mammograms have appeared in the news almost as much as Miley Cyrus—and they've been nearly as controversial. It seems like every week there's a new report that contradicts the last one. Start at 40! Start at 50! Get one every year! Every other year! Mammos are essential! Mammos are useless!

Wait, what?

The current controversy kicked off in 2009, when the U.S. Preventive Services Task Force (USPSTF) recommended that women of average risk start routine screening for breast cancer at 50 instead of 40—sparking a national outcry. Many organizations, including the American College of Obstetricians and Gynecologists (ACOG), disagreed—and in 2011, ACOG changed its guidelines to advise that women not only start screening at 40 but also do so every year instead of every other, as the group had previously advocated.

The headlines that followed made things even more unclear. Last September, researchers at Massachusetts General Hospital found evidence suggesting that screening does save lives: Out of 1,840 women in their study who were diagnosed with invasive breast cancer in their 40s, 77 percent of those who died hadn't had a mammogram in the two years before the cancer was detected. But in February, Canadian researchers released contradictory findings: After tracking nearly 90,000 women age 40 to 59 for 25 years, they found that those who had had regular mammograms weren't any less likely to die of breast cancer than those who had only breast exams. Then, in April, Harvard researchers, looking at 50-plus years of data, published a study that came to a mixed conclusion: Mammograms do save lives, but they're a flawed tool with hazards of their own.

Confused? We were, too. So we asked more than two dozen leading women's health doctors to tell us what they think. The overwhelming consensus: Start having mammograms at age 40 and get screened at least every other year (ideally yearly).

Why Mammos Are Under Fire
The USPSTF made its recommendations based on research suggesting that the gains of getting regular cancer-screening mammos in your 40s may not outweigh the risks. For one, younger women have lower odds of developing breast cancer, so they don't benefit as much from screening.

And some studies show that women in their 40s who get mammos are more likely to have false positives—suspicious findings that prove to be nothing—than women in their 50s, says Therese Bevers, MD, professor in the department of clinical cancer prevention at the University of Texas MD Anderson Cancer Center in Houston. Simple math dictates that the more you screen, the greater your chances of having a scare: The latest Harvard review showed that 61 percent of women in their 40s and 50s who are screened annually for 10 years will have at least one false positive at some point. "Each scare can cause stress, anxiety, expense and sometimes even biopsies," says Nancy Keating, MD, the study's co-author (who believes it's reasonable for women of average risk to start screening at age 50).

Yet false positives are not, many experts insist, a reason to delay screening. "Most of my patients feel they'd rather undergo some tests to find out if a mass is benign than miss one that's malignant," says Elisa Port, MD, chief of breast surgery and director of the Dubin Breast Center at Mount Sinai Hospital in New York City. In fact, a new study published in April in JAMA Internal Medicine found that women who'd had false positives were no less likely to say they intended to get another mammogram in the next two years, compared with those who got negative results.

A more troubling issue is overdiagnosis. Mammos sometimes detect lesions that would never progress to life-threatening cancer, such as some cases of ductal carcinoma in situ (DCIS), in which abnormal cells are confined to the breasts' milk ducts. But since doctors can't always tell at first which growths are bad news, most are treated as if potentially lethal—which means as many as 19 percent of cancers diagnosed during screening are treated with unneeded surgery, radiation and/or chemotherapy, Dr. Keating says.

"That's not a problem with screening," argues Carolyn D. Runowicz, MD, a professor of obstetrics and gynecology at Florida International University's Herbert Wertheim College of Medicine in Miami. "It's a problem with science, which hasn't evolved to the point where it can always distinguish between benign and serious conditions."

Next Page: The Case for Starting at 40 [ pagebreak ]
The Case for Starting at 40
While women in their 50s and 60s are far more likely to be struck by breast cancer, many 40-somethings get the disease: An estimated 51,680 women in their 40s were diagnosed in 2013, and nearly 3,800 died, per the American Cancer Society. For that reason alone, many doctors believe that women in this age group should line up for their mammos. Without them, a doctor's best tool is a clinical breast exam. But "by the time you can actually feel a mass," Dr. Bevers points out, "cancer is often fairly advanced."

And early detection is still the goal. "Some people argue that we don't need to worry anymore about catching cancer in its earliest stages, because treatments have become so much more effective," Dr. Runowicz says. "But those treatments come at a cost." The earlier you're diagnosed, the fewer toxic, invasive treatments you may have to endure, which can make a big difference to your well-being. "If a woman can avoid chemo or have a lumpectomy instead of a mastectomy, that's a very good thing." says Pamela Berens, MD, professor of obstetrics and gynecology at the University of Texas Health Science Center at Houston.

Early detection may be particularly crucial for women under 50, who often have more aggressive, fast-growing cancers, Dr. Berens says. That's why most of the doctors we spoke to advocate getting screened yearly. "We see interval cancers—ones that turn up between screenings— in some women even when we screen every year," Dr. Runowicz says. "If we wait longer, we're giving aggressive cancers even more time to become far more serious."

Studies look at huge populations to determine whether waiting an extra year is safe for the majority, adds Dennis Citrin, MD, a medical oncologist specializing in breast cancer at Cancer Treatment Centers of America in Zion, Ill. "But I don't treat populations. I treat individual women," he says. "And I don't want any of my patients to be the ones who are diagnosed late."

New Tech Changes the Game
One limitation of the Canadian study (the one that found that screening didn't save lives, contrary to previous research that said it reduces the risk of dying from the disease by 15 percent or more) is that it looked at women who had had mammos in the 1980s, when machines were far less sophisticated. "Think about how phones, computers and TVs have changed in the last 30 years," Dr. Citrin says. "It's the same with mammography."

Digital mammograms, introduced in 2000, detect more cancers than film mammos in women with dense breasts and those under 50. And there's some evidence that they don't find more low-grade DCIS—and so may not add to the problem of overdiagnosis. New 3-D mammography technology was approved by the FDA in 2011 and may be an improvement over digital.

"Clearly the solution to the overdiagnosis issue is developing better tools to determine which cancers are likely to be lethal," says Carol Lee, MD, chair of the Communications Committee of the Breast Imaging Commission of the American College of Radiology. With DCIS, for instance, researchers are examining biomarkers in the blood and tissue and using gene sequencing to sort out which lesions are most apt to progress to invasive cancer.

In the meantime, it's up to us to ask ourselves, How would I feel if my mammo found something that turned out to be nothing? Or if I put off the screening and my cancer was detected late? "Some women may want to wait to start screening till age 50, and many will do just fine," says Freya Schnabel, MD, director of breast surgery at the NYU Langone Medical Center. "But if you want to maximize the odds of early detection, your best bet is to get screened annually starting at 40."