L. Elmore1, A. D. Deshpande1, J. A. Margenthaler1 1Washington University,Surgery,St. Louis, MO, USA
Introduction: In the absence of lymph node involvement, tumor size is arguably the most important prognostic factor for women with breast cancer. Development of an optimal adjuvant treatment regimen for women with locally-advanced node-negative breast cancer is critical due to the risk of locoregional failure. Radiation therapy has been shown to improve locoregional control in selected populations of women with breast cancer but its efficacy in T3 node-negative breast cancer is controversial. We investigated patterns of post-mastectomy radiation therapy (PMRT) use and the survival impact of this treatment modality in women with T3 node-negative breast cancer.
Methods: A retrospective cohort study was conducted by identifying women with T3 node-negative breast cancer from the 1988-2009 Surveillance, Epidemiology and End Results (SEER) database. Our primary outcome variable was breast cancer-specific mortality. Several sociodemographic variables and tumor characteristics were obtained to evaluate patterns of use of adjuvant therapy. Survival curves were generated using the Kaplan-Meier method. Hazard ratios were computed using Cox proportional hazard analysis. Propensity score analysis was used to evaluate the effect of radiation on overall and breast cancer-specific mortality.
Results:We identified 2874 patients with T3 node-negative breast cancer. Within this cohort of women, 961 (33%) received PMRT and 1913 (67%) did not. Statistically significant differences were seen in adjuvant radiation therapy use based upon patient age, marital status, tumor grade, tumor size and receptor status (p<0.05 for all). Younger age at diagnosis, marriage, and grade 3 tumor pathology were associated with adjuvant therapy use. Tumor size >9cm was associated with decreased use of adjuvant radiation therapy. Analysis of overall mortality demonstrated lower mortality in the PMRT group in unadjusted analysis (cHR 0.718; 95% CI 0.614,0.840); however, adjusted hazard ratios demonstrated no difference in overall mortality (aHR 0.898; 95% CI 0.765, 1.054). Unadjusted analysis of breast-cancer specific mortality demonstrated no difference in those who received PMRT and those who did not (cHR 0.834; 95% CI 0.682,1.021). After adjusting for potential confounders using a propensity score analysis, again no significant difference in breast-cancer specific mortality was observed based on PMRT use (aHR 0.939; 95% CI 0.762, 1.157).
Conclusion:Analysis of the SEER database demonstrated that several patient and tumor characteristics are associated with use of adjuvant radiation therapy. Results of the current study indicate that receipt of PMRT does not affect breast-cancer specific or overall survival in women with T3 node-negative breast cancer.