Breast Cancer Screening

Breast Cancer Screening October 7, 2011 Donna Fitzpatrick-Lewis, Nicole Hodgson, Donna Ciliska, Leslea Peirson, Mary Gauld, Yan Yun Liu McMaster University Hamilton, Ontario, Canada.

Background
This systematic review is an update of the evidence since the 2001 Canadian Task Force recommendations on breast cancer screening.

Purpose
A decision was made to update the United States Preventive Services Task Force (USPSTF) 2009 review; therefore the purpose was the same as that review: to determine the effectiveness of mammography screening on decreasing breast cancer and all cause mortality among average-risk women between the ages of 40 and 49 and those 70 years and older; to determine the effectiveness of clinical breast examination (CBE) or breast self-examination (BSE) in decreasing mortality in average-risk women of the same age groups; and to determine the harms associated with mammography, CBE, and BSE. Additional contextual questions considered the costs associated with screening; patient preferences and values regarding breast screening; and particular subgroup information regarding the burden of breast cancer or rates of screening among Aboriginal women, rural or remote-residing women, and women of various ethnic backgrounds; and the optimal frequency of screening.

Data Sources
The search strategy from the USPSTF’s 2009 review of breast cancer screening was updated.Medline® and the Cochrane Database of Systematic Reviews were searched from December 2008 to October 2010 for studies in English and French. For patient preferences and values CINAHL and Medline were searched from 2000 to October 2010. Medline was searched back to 1950 for systematic reviews for subgroups. References of retrieved articles were checked, selected grey literature was searched for Canadian statistics, and some authors were contacted.

Study Selection
Randomized controlled trials and systematic reviews with breast cancer mortality or all cause mortality as outcomes for effectiveness of screening (mammography, CBE, or BSE) were included. For the literature on harms and on patient preferences and values, all study designs were included; for subgroups of interest, systematic reviews were included.

Data Abstraction
Relevant articles were abstracted. Study quality was assessed using GRADE.

Results
No new trials were found regarding mammography, CBE, or BSE on breast cancer mortality or all cause mortality. Seventeen new publications were identified and included: one systematic review of the effect of mammography on mortality; two systematic reviews and nine primary studies of harms; and five papers on costs. The search for information on patient preferences and values found three systematic reviews and 23 primary studies.

Data Synthesis
There were no new trials of mammography on breast cancer mortality; trials identified during the USPSTF search were summarized using the GRADE process. Of nine available trials, four were adequately randomized and five had methodological or reporting deficits related to randomization. In a meta-analysis of the eight studies (348,219 participants) of screening mammography in women aged 39–49 the pooled effect of screening versus no screening on breast cancer mortality was a relative risk (RR) of 0.85 (95% CI 0.75–0.96; I2=0%) after an overall median follow-up of 11.4 years. Pooled results from two trials showed that screening did not significantly reduce all cause mortality among 211,270 women aged 39–49 (RR 0.97, 95% CI 0.91–1.04;I2=0%). Meta-analysis of the two trials (17,646 participants) that reported results for women ≥70 years found that screening led to a nonsignificant reduction in breast cancer mortality (RR 0.68, 95% CI 0.45–1.01; I2=0%). The meta-analysis of seven studies of mammography screening for the 250,274 women aged 50–69 years found a reduction in breast cancer mortality (RR 0.79, 95% CI 0.68–0.90; I2=41%). Although the relative risk reductions were statistically significant for most age groups, the absolute magnitude of the reductions was small across all age groups. The effectiveness of BSE and CBE has not been established. Two studies of BSE from the USPSTFreview showed no difference in breast cancer mortality. Harms include false-positive rates of 6.5% for mammography and 8.7% for CBE and/or mammography. Approximately 28% of women aged 50-69 and 33% of women aged 40-49 screened with mammography will receive at least one false-positive result. The studies of patient preferences and values found that women value mammography for the perceived reduction in mortality; few women consider issues of harm arising from false-positives in making decisions about breast cancer screening. Aboriginal women and women who live in rural and remote geographies have less access to mammography services than do women in the general population.

Limitations
The search was updated based on the USPSTF review; therefore, EMBASE was not searched, and only articles in English and French were included. The searches for cost, patient values and preferences, and special populations were focused and not based on a full systematic review.

Conclusions
This updated meta-analysis of mammography screening trials indicates a reduction in breast cancer mortality for women aged 40–49 and a nonsignificant effect on breast cancer mortality for women ≥70 years. Pooled analyses confirm the previously reported reduction in breast cancer mortality for women aged 50–69 years. Future trials will be essential in assessing risk and benefit in screening the Canadian population and in determining the effect of newer technologies for breast imaging.

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