Geographic association between mammography use and mortality reduction in the US

Abstract

Background: Breast cancer mortality rates in women have been declining at the same time as breast cancer incidence rates, mammography rates and use of effective adjuvant therapy have been increasing. The objective of this study was to examine population data on breast cancer screening and breast cancer mortality to see if there is any geographic association between mammographic screening and breast cancer mortality reduction in the US, after adjusting for therapy use. Methods: Regression analysis of the estimated annual percent reduction of breast cancer mortality was performed on mammography use from the Behavioral Risk Factors Surveillance System (BRFSS) at state level. A secondary regression analysis on the SEER-11 region, at an aggregated Health Services Area (HSA) level, was carried out to adjust for use of adjuvant therapy. The annual percent change in the incidence of early stage cancer, calculated from SEER cancer data was used as a surrogate for mammography use. Adjuvant therapy use was estimated from SEER data and adjusted using the Patterns of Care data. Results: All the analyses showed a small but significant negative correlation between mammography usage and mortality reduction (correlation of −0.285, p-value 0.045) in breast cancer (state level) and change in ‘early’ stage breast cancer and mortality reduction (at HSA level) unadjusted (correlation of −0.307, p-value 0.065) and adjusted (partial correlation of −0.337, p-value 0.044) for adjuvant therapy use. Discussion: The results of the two analyses appear to show a moderate effect of mammography usage on decreasing breast cancer mortality in the US, which seems to support the conclusions of randomized mammographic screening trials. While randomized controlled trials are certainly the gold standard in appraising the efficacy of new screening or treatment modalities, such trials are conducted under standardized conditions and do not always reflect the effect of these interventions at population level. This paper attempts to examine population level effects through ecologic analyses. Results, however, need to be interpreted cautiously owing to the limitations and biases inherent in such analyses.