Breast cancer screening controversies

Abstract

Background: The Cochrane Collaborative, a respected independent review body, recently published a meta-analysis of the effectiveness of screening mammography in decreasing breast cancer mortality. Based on the results of two controlled trials they judged to be of medium validity, they concluded that screening mammography was unjustified. In contrast, the US Preventive Services Task Force recently updated their screening recommendations, and based on a meta-analysis of the same randomized controlled trials, they recommended screening mammography for all women starting at age 40 years. Additionally the Canadian Task Force on Preventive Health Care no longer recommends breast self-examination (BSE). This article reviews the controversies regarding breast cancer screening.

Methods: We performed a systematic review of the literature using keywords and cross-referencing articles. We also used automated data from the Breast Cancer Screening Program at Group Health Cooperative to determine the sensitivity of the clinical breast examination (CBE) at our institution. For the latter we included all cancers diagnosed within 1 year of a screening examination and then determined which of those had been found by CBE.

Results: Although most screening studies have shown that mammography decreases breast cancer death, there are controversies about the validity of some of the randomized controlled screening mammography trials. These controversies have led to different conclusions about the efficacy of screening mammography. Evidence is limited about the optimal interval for screening mammography. No studies have directly tested the efficacy of the CBE in decreasing breast cancer mortality. At Group Health Cooperative, 8% of all diagnosed breast cancers were found by the CBE alone (negative mammogram). Whether this 8% incremental increase in case finding leads to decreased breast cancer deaths is unknown. There is good evidence that training women to perform BSE does not increase breast cancer diagnoses or decrease breast cancer deaths.

Conclusion: There are limitations to randomized controlled trials and meta-analyses. The balance of the evidence still favors screening mammography in women aged 40 years and older at least every 2 years. The independent incremental benefit of the CBE, when added to mammography, in decreasing breast cancer mortality is unknown. Population-based education and training to do BSE are unlikely to lead to decreased breast cancer deaths. Many women find their own breast cancers, so women need to pay attention to symptoms or changes in their breasts.