Evidence based review of mammography screening for breast cancer

Gotzsche PC, Jorgensen KJ. “Screening for breast cancer with mammography.” Cochrane Database of Systematic Reviews. 2013 Jun 4;6:CD001877.

BACKGROUND: A variety of estimates of the benefits and harms of mammographic screening for breast cancer have been published and national policies vary.

OBJECTIVES: To assess the effect of screening for breast cancer with mammography on mortality and morbidity.

METHODS: We searched PubMed (22 November 2012) and the World Health Organization`s International Clinical Trials Registry Platform (22 November 2012).

SELECTION CRITERIA: Randomized trials comparing mammographic screening with no mammographic screening.

DATA COLLECTION AND ANALYSIS: Two authors independently extracted data. Study authors were contacted for additional information.

MAIN RESULTS: Eight eligible trials were identified. We excluded a trial because the randomization had failed to produce comparable groups.The eligible trials included 600,000 women in the analyses in the age range 39 to 74 years. Three trials with adequate randomization did not show a statistically significant reduction in breast cancer mortality at 13 years (relative risk (RR) 0.90, 95% confidence interval (CI) 0.79 to 1.02); four trials with sub-optimal randomization showed a significant reduction in breast cancer mortality with an RR of 0.75 (95% CI 0.67 to 0.83). The RR for all seven trials combined was 0.81 (95% CI 0.74 to 0.87). We found that breast cancer mortality was an unreliable outcome that was biased in favor of screening, mainly because of differential misclassification of cause of death. The trials with adequate randomization did not find an effect of screening on total cancer mortality, including breast cancer, after 10 years (RR 1.02, 95% CI 0.95 to 1.10) or on all-cause mortality after 13 years (RR 0.99, 95% CI 0.95 to 1.03).Total numbers of lumpectomies and mastectomies were significantly larger in the screened groups (RR 1.31, 95% CI 1.22 to 1.42), as were number of mastectomies (RR 1.20, 95% CI 1.08 to 1.32). The use of radiotherapy was similarly increased whereas there was no difference in the use of chemotherapy (data available in only two trials).
AUTHORS’ CONCLUSIONS:

If we assume that screening reduces breast cancer mortality by 15% and that overdiagnosis and overtreatment is at 30%, it means that for every 2000 women invited for screening throughout 10 years, one will avoid dying of breast cancer and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress including anxiety and uncertainty for years because of false positive findings. To help ensure that the women are fully informed before they decide whether or not to attend screening, we have written an evidence-based leaflet for lay people that is available in several languages on http://www.cochrane.dk. Because of substantial advances in treatment and greater breast cancer awareness since the trials were carried out, it is likely that the absolute effect of screening today is smaller than in the trials. Recent observational studies show more overdiagnosis than in the trials and very little or no reduction in the incidence of advanced cancers with screening.

Oncology – Breast:  This publication will undoubtedly be controversial and provocative. Why are the results of this meta-analysis so different from the conclusions and recommendations of other studies? The authors raise good arguments as to the probable lesser benefits of screening in today`s world with better awareness and more effective systemic therapies available; however, in my opinion, it would be premature to dismantle screening programs. The authors state that 50% of “early” breast cancers would never cause problems and lead to overdiagnosis and overtreatment. I am uncertain about the accuracy and evidence supporting this statement.

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