Background:

In 2009, the U.S. Preventive Services Task Force (USPSTF) recommended biennial screening mammography for women age 50 to 74 years, and based decisions for earlier screening on individual patient context and values. Evidence was insufficient to recommend screening beyond age 75.

Purpose:

To systematically update the 2009 USPSTF review on screening for breast cancer in average risk women age 40 years and older.

Data Sources:

The Cochrane Central Register of Controlled Trials and Cochrane Database of Systematic Reviews (through December 2014), Ovid MEDLINE (through December 2014), and reference lists were searched for relevant studies. Additional data were obtained from investigators of randomized trials and from the Breast Cancer Surveillance Consortium.

Study Selection:

Randomized controlled trials and observational studies of breast cancer screening in asymptomatic women age 40 and older reporting breast cancer mortality, all-cause mortality, advanced breast cancer, treatment morbidity, and the harms of screening.

Data Extraction:

One investigator abstracted data and a second investigator confirmed accuracy. Investigators independently dual-rated study quality and applicability using established criteria. Discrepancies were resolved through a consensus process.

Data Synthesis:

A meta-analysis of screening trials with updated data from the Canadian (CNBSS-1 and CNBSS-2), Swedish Two-County Study, and Age trials indicated breast cancer mortality reductions for age 39 to 49 years (relative risk [RR] 0.88; 95% confidence interval [CI], 0.73 to 1.003; 9 trials; 4 deaths prevented/10,000 over 10 years); 50 to 59 years (RR 0.86 [95% CI, 0.68 to 0.97]; 7 trials; 8/10,000); 60 to 69 years (RR 0.67 [95% CI, 0.54 to 0.83]; 21/10,000); and 70 to 74 years (RR 0.80 [95% CI, 0.51 to 1.28]; 3 trials; 13/10,000). Risk reduction was 25 to 31 percent for women age 50 to 69 years across several observational studies, with similar reductions for women age 40 to 49 in two studies. Trials indicated no statistically significant reductions in all-cause mortality with screening. Risk for higher-stage breast cancer was reduced for age 50 years and older (RR 0.62 [95% CI, 0.46 to 0.83]; 3 trials), but not for age 39 to 49 years (RR 0.98 [95% CI, 0.74 to 1.37]; 4 trials). The majority of cases from screening were ductal carcinoma in situ and early stage, and screening resulted in more mastectomies (RR 1.20 [95% CI, 1.11 to 1.30]; 5 trials) and radiation (RR 1.32 [95% CI, 1.16 to 1.50]; 2 trials).

Younger women and those with risk factors had more false-positive results and recommendations for additional imaging and biopsies. Cumulative rates for false-positive mammography results over 10 years were 61 percent for annual and 42 percent for biennial screening; rates for biopsy were 7 to 9 percent for annual and 5 to 6 percent for biennial screening. Estimates of overdiagnosis ranged from 11 to 22 percent in trials; and 1 to 10 percent in observational studies. Some women with false-positive results or pain experienced distress and were less likely to return for their next mammogram. Tomosynthesis with mammography reduced recalls (16/1000), but increased biopsies (1.3/1000) and cancer detection (1.2/1,000). The number of deaths due to radiation induced cancer from screening with digital mammography was estimated through modeling as between 2 to 11 per 100,000 depending on age at onset and screening intervals.

Limitations:

Limited to English-language articles; the number, quality, and applicability of studies varied widely. Trials of mammography screening reflect imaging technologies and cancer treatment therapies that are not currently in use. Studies are lacking on screening effectiveness based on risk factors, intervals, and modalities; and on screening modalities relevant to women who are not high-risk.

Conclusions:

Breast cancer mortality is reduced with mammography screening, although estimates are of borderline statistical significance, the magnitudes of effect are small for younger ages, and results vary depending on how cases were accrued in trials. Higher stage tumors are also reduced with screening for age 50 years and older. False-positive results are common in all age groups, and are higher for younger women and those with risk factors. Approximately 11 to 22 percent of cases may be overdiagnosed. Observational studies indicate that tomosynthesis with mammography reduces recalls, but increases biopsies and cancer detection. Mammography screening at any age is a tradeoff of a continuum of benefits and harms.