In 2009, 192,370 U.S. women were diagnosed with breast cancer, as were 1,910 men.3 A total of 40,170 women and 440 men died of the disease that year. The high incidence of breast cancer, combined with strong public messages surrounding the importance of early detection, has created a high demand for mammography and other screening technologies designed to detect disease at an early and treatable phase.
The medical community has struggled to educate women about cancer risk and ensure access to and funding for early detection. The news that mammography screening beginning at age 40 might not be best for all patients was therefore greeted with shock and skepticism by health-care professionals and the lay public alike.
The USPSTF characteristically ranks its recommendations according to the strength of the data analyzed. The task force gave biennial mammography for women aged 50 to 74 years a B grade, meaning that its members are moderately to highly certain of the technique’s routine benefit.
As for screening mammography before age 50 years, the USPSTF issued a C grade; this ranking indicates that the service should not be provided routinely but only when “other considerations” (e.g., elevated individual risk or strong patient preference) dictate.
The USPSTF also advised that there is insufficient evidence to recommend for or against routine screening mammography for women older than age 75 years. When insufficient evidence exists, the task force encourages that decisions be made on an individual basis and that patients be educated as to the benefits and harms of the procedure.
Although the USPSTF recommendations were widely regarded as surprising news, the understanding that the benefits of mammography vary by age is nothing new. Advancing age, after all, is the most significant determinant of a woman’s breast-cancer risk.
In 1997, biostatistician Virginia Ernster, PhD, chronicled the findings of the NIH consensus development conference on breast-cancer screening for women aged 40 to 49 years.4 NIH experts had determined that “data on the benefits and risks of screening mammography for women aged 40 through 49 are sufficiently mixed that informed decision making, rather than a blanket recommendation for all women, is an appropriate course of action.” This view, then as now, divided the medical community.
In the 13 years since that NIH conference, numerous studies have affirmed that the usefulness of mammography increases with age, especially from ages 50 to 65 years. The abundance of existing studies point to clear benefit for women aged 50 years and older but are ambivalent about screening in average-risk women between the ages of 40 and 50.5
Additionally, the cost-effectiveness of screening for women in their 40s is considerably lower than that for women aged 50 years and older.6 The strongest evidence of mammography’s benefit exists for women aged 60 to 69 years. No women older than age 75 years have participated in randomized clinical trials for breast-cancer screening.
In shaping its recommendations for women in their 40s, the USPSTF sought to incorporate data from studies conducted since the recommendations’ last iteration in 2002. Some of the data considered came from a 2006 study that quantified the reduction in 10-year mortality attributable to annual mammograms among women in their 40s.
The authors found that the benefit, while real, was not statistically significant.7 According to a recent systematic review cited by the USPSTF, one breast-cancer death could be prevented by screening 1,904 women aged 40 to 49 years; in contrast, only 1,339 women aged 50 to 59 years have to be screened to prevent one death.8 Modeling studies that appeared in the same issue of Annals of Internal Medicine as the updated USPSTF recommendations confirmed that in six of the eight most effective strategies analyzed, women began screening at age 50 years.9
Mammography currently represents our best method for breast-cancer screening but is by no means a flawless technology. With a high rate of false positives, mammograms can result in unnecessary biopsies and even in the treatment of insignificant growths that might have regressed otherwise. According to one study, a third of women screened with mammograms and clinical breast exams over a 10-year period would undergo follow-up for false-positive results.10
Nevertheless, most women surveyed for a 2004 study consider the risk of false-positive findings acceptable in order to detect early cancers.11 However, these false positives may result in disfiguring procedures, costly treatments with a range of side effects, and a high burden of anxiety.
According to a 2009 study, women with uncertain breast biopsy results had patterns of cortisol secretion comparable to those of women with a diagnosis of cancer.12 Elevated cortisol, indicative of emotional and/or physical stress, can contribute to chronic and episodic illness.
Much of the confusion regarding the utility of early and frequent breast-cancer screening can be attributed to the ongoing controversy surrounding ductal carcinoma in situ (DCIS). DCIS is a common, noninvasive breast condition that can progress to invasive breast cancer when left untreated.
It is generally diagnosed by mammography and treated with surgery and/or radiation, often followed by hormone therapy. Many cases of DCIS will not develop into cancer or will grow extremely slowly, leading some experts to worry that DCIS may currently be overdiagnosed or overtreated, particularly in younger women.
While many argue that false-positive tests and their subsequent follow-up are a small price to pay for the security of thorough screening, mammography can have disappointingly limited sensitivity, especially in younger women with dense breasts. Estimates of the test’s sensitivity generally fall near the 75% mark. According to data from the National Cancer Institute, younger women — especially those with dense breasts or fast-growing tumors—are more likely than older women to be diagnosed with breast cancer following a negative mammogram.13
Studies also show that women younger than age 50 benefit from screening by digital rather than film mammography, but the USPSTF regards the present evidence as insufficient for a large-scale recommendation favoring digital mammography.14
Importantly, screening recommendations apply only to average-risk patients. Women with a family history of breast cancer or other risk factors should have a personalized schedule. High-risk women also may be candidates for MRI; the sensitivity of MRI has been reported to be as high as 100% in some studies. However, the procedure is costly.15