Commentary

Sorting through the recent controversies in breast cancer screening

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Editor’s Note: This commentary, written by members of the Cleveland Clinic Breast Cancer Screening Task Force, was not independently peer-reviewed.

In November 2009, the US Preventive Services Task Force (USPSTF) announced its new guidelines for breast cancer screening—and created an instant controversy by suggesting that fewer screening tests be done.1

The November 2009 update recommended that most women wait until age 50 to get their first screening mammogram instead of getting it at age 40, that they get a mammogram every other year instead of every year, and that physicians not teach their patients breast self-examination anymore. However, on December 4, 2009, the USPSTF members voted to modify the recommendation for women under age 50, stating that the decision to start screening mammography every 2 years should be individualized, taking into account the patient’s preferences after being apprised of the possible benefits and harms.2

Various professional and advocacy groups have reacted differently to the new guidelines, and as a result, women are unsure about the optimal screening for breast cancer.

NEW GUIDELINES ARE BASED ON TWO STUDIES

The USPSTF commissioned two studies, which it used to formulate the new recommendations.3,4 Its goal was to evaluate the current evidence for the efficacy of several screening tests and schedules in reducing breast cancer mortality rates.

An updated systematic review

Nelson et al3 performed a systematic review of studies of the benefit and harm of screening with mammography, clinical breast examination, and breast self-examination.

Screening mammography continued to demonstrate a reduction in deaths due to breast cancer. The risk reduction ranged from 14% to 32% in women age 50 to 69. Similarly, it was calculated to reduce the incidence of deaths due to breast cancer by 15% in women age 39 to 49. However, this younger age group has a relatively low incidence of breast cancer, and therefore, according to this analysis, 556 women need to undergo one round of screening to detect one case of invasive breast cancer, and 1,904 women need to be offered screening (over several rounds, which varied by trial) to prevent one breast cancer death.3

Most of the harm of screening in the 39-to-49-year age category was due to false-positive results, which were more common in this group than in older women. The authors calculated that after every round of screening mammography, about 84 of every 1,000 women in the younger age category need additional imaging and about 9 need a biopsy. The issue of overdiagnosis (detection of cancers that would have never been a problem in one’s lifetime) was not specifically addressed for this age category, and in different studies, estimates of overdiagnosis rates for all age groups varied widely, from less than 1% to 30%.

Beyond age 70, the authors reported the data insufficient for evaluating the benefit and harm of screening mammography.

Breast self-examination was found to offer no benefit, based largely on two randomized studies, one in St. Petersburg, Russia,5 and the other in Shanghai, China,6 both places where screening mammography was not routinely offered. These studies and one observational study in the United States7 failed to show a reduction in breast cancer mortality rates with breast self-examination.

Clinical breast examination (ie, by a health care provider) lacked sufficient data to draw conclusions.

A study based on statistical models of mammography

Mandelblatt et al4 used statistical modeling to estimate the effect of mammographic screening at various ages and at different intervals.

The authors used six statistical models previously shown to give similar qualitative estimates of the contribution of screening in reducing breast cancer mortality rates. They estimated the number of mammograms required relative to the number of cancers detected, the number of breast cancer deaths prevented, and the harms (false-positive mammograms, unnecessary biopsies, and overdiagnosis) incurred with 20 different screening strategies, ie, screening with different starting and stopping ages and at intervals of either 1 or 2 years.

They estimated that screening every other year would achieve most of the benefit of screening every year, with less harm. Looking at the different strategies and models, on average, biennial screening would, by their calculations, achieve about 81% of the mortality reduction achieved with annual screening. Compared with screening women ages 50 to 69 only, extending screening to women age 40 to 49 would reduce the cancer mortality rate by 3% more, while extending it up to age 79 would reduce it by another 7% to 8%.

In terms of harm, the models predicted more false-positive studies if screening were started before age 50 and if it were done annually rather than biennially. They also predicted that more unnecessary biopsies would be done with annual screening than with screening every 2 years. The models suggested that the risk for overdiagnosis was higher in older age groups because of higher rates of death from causes other than breast cancer, and that the overdiagnosis rate was also somewhat higher with annual than with 2-year screening.

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