A woman receives a mammogram.

For decades, women have been urged to have regular mammograms, breast X-rays that help detect lumps that may signal cancer. But cancer experts currently don't agree on when women should begin to have this breast cancer screening test, or how often to do so.

For instance, the U.S. Preventive Services Task Force (USPSTF), an independent panel of medical experts that evaluates preventive medical services, says women at average breast cancer risk should start screenings at age 50.

But the American Cancer Society (ACS) recommends starting at 45, while the American College of Radiology (ACR) advises beginning at age 40.

And the American College of Obstetricians and Gynecologists (ACOG) says women should start screening no later than age 50 but with the choice to begin sooner.

Why the different advice? In part, it’s because these expert groups may evaluate scientific studies on mammography differently, some placing more weight on the benefits of mammography and some emphasizing the screening’s potential downsides, according to the American College of Physicians (ACP).

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They may also differ in the types of studies they rely on or on how to grapple with issues of cost when writing screening recommendations.

The result: “Both patients and clinicians are frustrated and sometimes confused,” says Joann Elmore, M.D., M.P.H., professor of medicine at the David Geffen School of Medicine at UCLA, and director for the UCLA National Clinician Scholars Program.

In addition, like all screening tests, mammograms themselves have their pros and cons.

Here, what to know about mammography, what the various recommendations may mean for you, and how to work with your doctor to make the best decision for yourself. 

Understanding Testing's Benefits and Harms

Death rates from breast cancer have been decreasing for several decades, and evidence suggests that the introduction of breast cancer screening programs is partially responsible—along with the development of more effective treatments. 

For instance, a 2018 study on Swedish cancer patients, published in the journal Cancer, found that women who participated in a screening program were less likely to die of breast cancer than women who skipped screening.

But some experts think another factor is more significant. “In the pre-chemotherapy era, most of the reduction in [breast cancer] mortality was attributable to screening,” Barry S. Kramer, M.D., M.P.H., a consultant to the National Cancer Institute (NCI) Division of Cancer Control and Population Sciences, and former director of the NCI Division of Cancer Prevention. Today, he says, the main driver is improvements in cancer treatments.

And the likelihood that screening will help prevent a breast cancer death is admittedly small, according to the USPSTF. Estimates vary, but the Task Force’s analysis of randomized controlled trials found that screening 10,000 women ages 60 to 69 regularly for a decade led to 21 fewer women dying of breast cancer.

Plus, plenty of research has found that breast cancer screening can carry harms along with benefits. One is the possibility for false positives, or findings that suggest cancer but turn out to be benign. (Mammograms may also, but more rarely, lead to false negatives—a missed cancer.)

According to the USPSTF, among 10,000 women age 60 to 69, some 808 will receive a false positive result after one screening. 

A false positive can lead to anxiety and unnecessary follow-up testing, including biopsies, which are uncomfortable and carry a small risk of infection.

Another possible harm is overdiagnosis, the finding of cancers that will never go on to be life-threatening. 

Scientists aren't sure how common this is, because there’s no way to know which cancers are potentially deadly, and which will never progress.

The USPSTF estimates that at least 1 in 8 tumors detected by mammography would never have been lethal, and that for every woman whose life is saved by mammography, two or three will be treated without good reason. And breast cancer treatments, such as chemotherapy, can have powerful and lasting side effects.

Certain people may be at greater risk for some screening harms than others. For example, if you’ve been told you have dense breasts, you’re more likely than others to experience a false negative, false positive, or unnecessary breast biopsy, according to the USPSTF. Getting screened at younger ages, such as in your 40s, also makes you more likely to receive a false positive.

What to Discuss With Your Doctor

So, what should you do? In light of the complexity of this issue, women and their doctors should use a process called shared decision-making, says Ana María López, M.D., M.P.H., immediate past president of the American College of Physicians (ACP).

This means considering the harms and benefits of mammography, as well as your own preferences, and having a thorough discussion of your personal health background as well as your family’s health history.

The last two help your doctor give you an idea of your overall breast cancer risk. That's essential because the various expert recommendations are only for women at average or slightly elevated risk.

(Factors for a slightly higher risk of breast cancer include the use of hormone replacement therapy, menstrual periods that began before age 12 or continued after age 55, a history of noncancerous conditions such as dense breasts, obesity, smoking, and excessive alcohol consumption.)

If you're at high risk—factors that may put you in that category can include a personal or strong family history of breast cancer, carrying a BRCA1 or BRCA2 genetic mutation, and a history of multiple chest X-rays or radiation treatments to the chest—you'll need to follow a different screening plan than other women do. Your doctor can help you map it out.

The American Cancer Society (ACR), for example, offers guidelines for women whose lifetime risk of breast cancer is calculated to be about 20 percent or higher. (The average lifetime risk is about 12 percent, according to the National Cancer Institute.) These guidelines include receiving a breast MRI and mammogram yearly starting at age 30. You may even be eligible for clinical trials of new types of screening, López says.

For women at average or slightly elevated risk of breast cancer,  the ACP recently released new guidance that synthesizes the different sets of recommendations into a few simple pieces of advice. To create the guidelines, the organization evaluated and scored each set of advice, using criteria such as the rigor of the science involved in their development, clarity, and lack of conflicts of interest among its authors.

You can use the ACP's guidance during a discussion with your doctor, and to help you answer the four key questions below.

1. When Should You Start Screening?

What the ACP guidance says: Women ages 40 to 49 should have the option for breast cancer screening, and doctors should discuss the harms and benefits of screening during these years. Healthcare providers should start offering screening to women starting at age 50.

What else to consider: Age is the most important risk factor for breast cancer for most women, and the greatest benefits from screening are seen in women in their 60s, according to the USPSTF. Starting screening at age 50 is when the growing risk of breast cancer likely outweighs the risks of screening, the Task Force and ACP say.

Still, the advice here varies. The ACS recommends beginning screening at age 45, while ACR says to start at 40. “We certainly believe that the benefits of screening far outweigh any of the potential harms,” says Geraldine McGinty, M.D., M.B.A., chair of the board of chancellors for the ACR.

Keep in mind that the earlier you start screening, the more likely you are to have a false alarm.

2. How Often Should You Have a Mammogram?

What the ACP guidance says: Screening should be offered every other year from ages 50 to 74.

What else to consider: The ACP guidance is in line with that of the USPSTF, while the ACS says that screening should be done yearly starting at age 45, and every other year starting at age 55. The ACR recommends screening every year.

ACOG says that whether you have a screening every year or every two years should be a matter of preference, based on shared decision-making with your doctor. Keep in mind that the more frequently you get screened, the more likely you are to experience related harms such as overdiagnosis.

3. When Should You Stop?

What the ACP guidance says: There’s no need to screen women ages 75 and older, or those who have a life expectancy of 10 years or fewer.

What else to consider: The last time the USPSTF addressed this question, in 2016, it concluded there wasn’t enough evidence to make a definitive recommendation on breast cancer screening for people 75 and older. ACOG says women 75 and older should talk with their doctor about whether testing continues to make sense for them, while the ACS says anyone who expects to live 10 more years should continue screening.

4. What About Breast Exams?

What the ACP guidance says: There’s no need for doctors to perform routine clinical breast exams. 

What else to consider: There’s little evidence that having your breasts checked by a physician reduces the risk of dying from breast cancer. Major groups generally don’t recommend this exam, though ACOG says it can be offered as an option every one to three years for women ages 25 to 29, and yearly for women 40 and older. 

And you don’t need to regularly examine your own breasts, but being aware of how your body normally feels is a good idea. “I still think it’s important for women to have a general sense of the normal contour of their own breasts,” Elmore says. “Because a high proportion of breast cancers are still detected by the women themselves, not by screening.”