New mammography guidelines call for starting later and screening less often

Women can wait until age 45 to start getting annual mammograms and cut back to every other year once they turn 55, according to new breast cancer screening guidelines from the American Cancer Society.

The recommendations, published in yesterday's issue of The Journal of the American Medical Association, are a major shift from the organization's previous guidelines, which advised women to get annual mammograms starting at age 40. They are intended for women with an average risk of breast cancer, meaning no family history of breast cancer or prior radiation treatment to the chest.

These changes reflect accumulating data showing that for women younger than 45, the harms of mammography screening likely outweigh the benefits, according to Dr. Nancy Keating, professor of health care policy and medicine at Harvard Medical School who coauthored an editorial discussing the new guidelines.

Making sense of the new guidelines

"For an average-risk woman in her early 40s, the risk of breast cancer is less than one in 100, or about 0.7%," says Dr. Keating. That's a lot lower than most women believe, partly because many women have heard the statistic that one in eight women will get breast cancer. But that statistic is a lifetime risk and applies only to 85-year-old women.

Women also tend to overestimate the benefits of mammography. We're told that mammography saves lives. In fact, mammography only reduces the relative risk of dying by about 20% overall, and by just 15% for women in their 40s, Dr. Keating explains.

"If we screen 10,000 women in their 40s every year for 10 years, we'll find about 190 to 200 cases of breast cancer. About 30 women will die of breast cancer regardless of the mammogram, and about five will have their lives saved because of the mammogram," says Dr. Keating. So the benefits of mammography in younger women are real, but quite small.

What about the harms? Of those 10,000 women, as many as 6,000 will be called back for a second mammogram because the radiologist saw a suspicious area. Between 700 and 1,000 will undergo a biopsy that ends up not being cancer. These biopsies are stressful, uncomfortable, and inconvenient. But they aren't the biggest problem.

The chief harm is overdiagnosis, which means being diagnosed with a cancer that never would have caused any health problems if left alone. Because doctors can't distinguish these slow-growing, low-risk tumors from more dangerous ones, some women end up receiving surgery, chemotherapy, and radiation that might not have actually been necessary. There's a great deal of uncertainty about how much overdiagnosis exists, but the best estimate to date is that it applies to about 19% of all breast cancers. That translates to 36 of the 190 cancers diagnosed in the example of 10,000 women.

The risk of breast cancer rises with age, so it might seem counterintuitive that the recommendations call for less-frequent mammograms once women hit their mid-50s. But older women tend to have less aggressive tumors than women who are diagnosed at younger ages. Getting a mammogram at two-year intervals lowers the harms while still reaping the benefits of the test, Dr. Keating explains.

While the previous guidelines advised women to keep getting mammograms as long as they're in good health, the new ones add another stipulation: a life expectancy of at least 10 years. This reflects the understanding that for most women age 70 or older and for those who have other illnesses, finding a breast cancer and treating it is unlikely to change their lifespan. (In the United States, women live to age 81, on average.) This recommendation may prevent overdiagnosis in older women.

What the new guidelines might mean for you

Women should discuss their own situation and preferences with their health care provider, Dr. Keating says. For her own patients, she uses the National Cancer Institute's Breast Cancer Risk Assessment Tool to calculate their risk and talks to them about their family history. For those with a low or average risk, she has them consider two questions: How do you feel about being diagnosed and treated for a cancer that, perhaps, you never needed to know about? How would you feel if you were diagnosed with breast cancer and hadn't had a mammogram?

"Would you be up at night wondering, is there anything I could have done that might have lowered my risk? For those people who aren't comfortable with a small risk, I'd say go ahead and get the mammogram," says Dr. Keating.