January 21, 2019
Mammogram Advice: A Moving Target

Mammogram Advice: A Moving Target

by Berkeley Wellness

There was a firestorm of protest in 2009 when the influential U.S. Preventive Services Task Force changed its mammogram recommen­dations—advising women between the ages of 50 and 74 who are at average risk for breast can­cer to be screened every two years (bienni­ally) instead of annually—and reaffirmed that women in their forties should not be screened routinely. Two years later, the Task Force’s Canadian counterpart went even fur­ther and recommended mammograms only every two to three years for women over 50, similar to guidelines of many other countries.

One of the groups that objected to the U.S. Task Force’s relaxed recommendations was the American Cancer Society (ACS), which long advised annual screening starting at age 40. In October 2015, however, the ACS announced that, after reviewing the research, it had modified its own recommendations, moving them somewhat closer to those of the Task Force. It did this, it said, to better balance the potential benefit of early detec­tion against the now-clearer evidence about the risks of false alarms and overtreatment.

Here are the new ACS guidelines for women at average risk:

  • Ages 40 to 44: Annual mammo­grams are now optional.
  • Ages 45 to 54: Women should start annual mammography at age 45.
  • Ages 55 and older: Women can tran­sition to having mammograms every other year, though they may choose to continue annual screening. One rationale was that cancers tend to grow slowly and are less aggressive in postmenopausal women.
  • Older ages: Screen­ing should continue as long as a woman is in good health, with a life expectancy of at least 10 years.
  • Clinical breast exams done by health profes­sionals are no longer recommended because of the “absence of clear evidence” that they add significantly to breast cancer detection beyond mammography; they also increase false-positives. While monthly self-exams are not advised either, women should be familiar with how their breasts normally look and feel and report changes to their health care provid­ers right away, the ACS advises.

Earlier in 2015, the Task Force, which periodically updates its positions, released slightly softened draft guidelines for mam­mography. These make it clearer that women in their forties may also want to be screened every two years, depending on their indi­vidual risk factors and personal preferences. The Task Force still offers no advice for women over 75 because research is lacking.

Meanwhile, several other medical groups, including the American College of Obstet­rics and Gynecology and the American College of Radiology, continue to recom­mend annual mammograms starting at 40.

Keep in mind that all “screening” recom­mendations pertain only to women at aver­age risk. Women at higher risk (because of family or personal history or certain genetic mutations) need earlier and more frequent screening based upon professional advice.

Why can’t the experts agree?

Nearly every statistic regarding mammo­grams is in dispute, and experts often point to different data to support their positions. There’s no lack of studies (many observa­tional), but none provide definitive answers. Part of the problem is that mammography is an imperfect screening test, closer to PSA blood tests (for prostate cancer) in its uncer­tainties than to Pap tests (for cervical cancer).

Most research suggests that routine mammography can reduce the risk of dying from breast cancer by anywhere from 10 to 25 percent. While that adds up to thousands of lives saved, many women still die from breast cancer despite being screened. And what about the harms experienced by the untold number of women who have false alarms and unnecessary treatment?

The average age for developing breast cancer is about 61. The risk increases with age, so the value of mammography also increases. The specific numbers have been debated, depending on which statistical models the experts use, but according to the Task Force, to save one life among women in their fifties, about 1,250 women must be screened for 10 years. That means tens of thousands of mammograms, which result in thousands of false alarms, hundreds of biopsies, and many cancers treated as if they were life-threatening when they are not.

Because breast cancer rates increase with age, fewer women in their sixties need to be screened to save one life. But com­pared to those in their fifties, about twice as many women in their forties would need to be screened to save one life, with even more false alarms—largely because younger women tend to have denser breasts, making it harder to interpret mammograms.

More about the potential harms

The most common harm from screening, called a false-positive, occurs when a mam­mogram mistakenly suggests that breast cancer may be present. This leads to follow-up imaging and often biopsies. Such false alarms can cause needless anxiety, though being aware that this occurs so frequently can help women cope better with the stress.

More serious are false-negatives, can­cers that are missed by mammography, some of which turn out to be lethal.

The most common serious harm is overdiagnosis, which occurs when a woman is found to have a small cancer or precan­cerous lesion (notably ductal carcinoma in situ, or DCIS) that would grow slowly or not at all and never become life-threatening. Currently, there is no way to know whether a localized cancer or precancerous growth will progress, so women diagnosed with breast cancer (and their health care provid­ers) are rarely willing to take a “wait and see” approach. Almost all are treated via surgery, chemotherapy, medication, or radi­ation, which can have significant harms.

Estimates vary dramatically about how often overdiagnosis and overtreatment occur. Improved sensitivity of mammogra­phy has contributed to increasing rates of overdiagnosis. According to the Task Force, about “one out of every five women diag­nosed by screening mammography and treated for breast cancer is being treated for cancer that would never have been discov­ered or caused her health problems.” Some experts believe the overdiagnosis rate may be as high as 50 percent.

Mammography: Is Every 2 Years Enough?

It may seem like getting screened for breast cancer every two years rather than annually could delay cancer diagnosis until tumors are at a more dangerous stage, thus endangering women’s lives. But several studies suggest that this is not the case.

Our advice

The fact that these expert groups can’t agree underscores the uncertainty and com­plexity of the data about mammography. The ACS has positioned itself somewhere in the middle between the Task Force’s rec­ommendation for biennial screening starting at age 50 and other groups’ continued rec­ommendation for annual screening starting at 40. While we still think that the Task Force’s guidelines make sense, the new ones from the ACS are a reasonable alternative.

Both the ACS and the Task Force now emphasize that women should consider their “values and preferences”—along with clinical guidance—when weighing the potential benefits and harms of various mammography schedules. Women will come to different decisions.

The ACS encourages women at average risk to have an initial discussion about screening with a health care provider at around age 40. They should be provided with information about their risk factors and about the benefits, limitations, and potential harms of mammography screening.

Women, working with their health care providers, need to decide which screening approach is best for them. For instance, if you value any chance of additionally reduc­ing your risk of dying from breast cancer, however small, you may decide to start screening at 40, opt for annual rather than biennial screenings (particularly before menopause), and request clinical breast exams, even though these choices increase the chances of false alarms and overtreat­ment. If you put more weight on reducing the risk of overdiagnosis and unnecessary treatment, biennial mammography starting at 50 is likely to be your best option.

Also see Re-examining the Breast Self-Exam.

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