Mammography Screening Guidelines

By OBOS Common Medical Conditions Contributors | October 15, 2011
Last Revised on Apr 23, 2014

All experts agree that mammograms can find breast cancers when they are small, are more curable, and need less treatment. But there is disagreement over how many are found or missed, how many are successfully treated when found, how many don’t need treatment at all, when to begin a regular mammogram schedule, and when to end it.

Weighing your personal preferences and concerns along with the recommendations of experts can be confusing and stressful, especially if you have personal risk factors or friends or relatives who have faced breast cancer. Nevertheless, informed deliberation will help you make the best decision for you.

Screening for Women Ages 40 to 49

The United States Preventive Services Task Force (USPSTF), a highly respected expert group, issued new guidelines in November 2009 recommending that women ages 40-49 group discuss with their clinicians when to start screening and whether to begin screening at age 40 after considering the benefits and risks and discussing personal preferences.

In doing so, the USPSTF retracted its previous guideline for this age group, which recommended routine (that is, automatic) screening every one to two years starting at age 40. The American Cancer Society (ACS) and the American College of Radiology (ACR), however, both continue to recommend routine screening every year starting at age 40 for all women.

There is agreement that mammography reduces death from breast cancer, even in women between the ages of 40 and 49. The USPSTF agreed that screening in this age group was responsible for at least a 15 percent decrease in mortality. So why the different recommendations?

The USPSTF used a rigorous method of evaluating mammography studies. It relied almost exclusively on prospective randomized trials comparing death rates from breast cancer in those randomized for screening against those randomized for observation only. Since the benefits of screening mammography have been widely acknowledged, only one randomized trial started during the last 20 years (because randomizing would have to assign some women to “no mammography,” which most researchers would consider unethical).

Critics of the USPSTF position assert that the weight of the USPSTF review is based on radiology studies that are out of date, but other experts dismiss this criticism. A long-term study published in February 2014 added to the evidence that some women — including those in their forties — do not benefit from screening mammograms.

In addition, different expert groups give different weight to the factors against and for routinely screening 40- to 49-year-old women.

Factors against routine screening starting at age 40

Breast cancer is much less common in this group than in older women; the number of false-positive tests (in which the mammogram suggests a woman has cancer, but a biopsy shows no cancer) is higher for younger women; and starting mammograms at 40 would mean having exams every two years for an average of 34 years. Over a lifetime, a woman’s chances of needing a biopsy to prove she didn’t have breast cancer might be as high as 50 percent.

Factors for routine screening in women starting at age 40

Cancers that are found in this age group tend to be more aggressive than those found in older women, and screening done every year, instead of every two years, may catch more of these aggressive cancers. While women may have to endure more biopsies, or anxiety with false-positive diagnoses, not getting screened can also produce anxiety.

It may be helpful to consider the comment of Dr. Ned Calogne, who chaired the USPSTF:

If I take 1,000 women age 40, over their lifetimes, 30 of them will die from breast cancer if we do no screening. If I screen every one of those women beginning at age 50 until she’s 74, we reduce the deaths from 30 to 23. And if I reach down and screen them in their forties, I can increase that by one additional life saved—at best.

Most experts agree that if a woman between the ages of 40 and 49 is identified as being at high risk, she should be regularly screened.

Screening for Women Age 50 to 74

All experts agree that women age 50 to 74 should be screened regularly. Some experts say women in this group should be screened every year; others say every one or two years.

The USPSTF proposes screening every two years. It argues that the additional lives saved by screening yearly are not enough to justify an annual procedure. Screening at two-year intervals would preserve 81 percent of breast cancer mortality reduction seen with screening at one-year intervals.

The American Cancer Society and the American College of Radiology recommend screening every year. They argue that the 19 percent increase in breast cancer deaths that comes with screening only every two years is not acceptable.

Screening for Women Over Age 74

The USPSTF makes no recommendations, because there are no randomized studies for this age group. The ACS and the ACR recommend annual screening as long as a woman has a life expectancy of five to seven years (most experts believe that the benefits of mammography compared with no mammography show up only after five years). They also note that it is easier to find breast cancer in older breasts and breast cancer risk increases with age. They also believe that the risks of screening are small.

The decision to screen or not screen in this age group, all agree, should rest on a discussion with one’s clinician/primary care provider. Whether it’s better to be screened every year or every two years is disputed. The incidence of breast cancer continues to increase into one’s 80s, although most of these breast cancers are not as aggressive as those found in younger women.