P3-13-11: Survival Benefit Associated with Post-Mastectomy Radiation for Node-Positive, Intermediate-Risk Breast Cancer Patients: Results of a Study from the SEER Registry Data.

Abstract

Abstract Background The role of post-mastectomy radiation therapy (PMRT) for breast cancer patients with intermediate-risk (1-3 positive nodes) disease remains controversial. This Surveillance, Epidemiology, and End Results (SEER) study investigated the impact of PMRT in the intermediate-risk breast cancer patient population on cause-specific survival (CSS) and overall survival (OS). The study also investigated the impact of estrogen receptor (ER) status, which has been reported in the SEER database since 2004, on the impact of PMRT in this patient population on CSS and OS. Methods: The SEER database was used to identify all breast cancer patients who were treated between 2004–2007, who had undergone mastectomy, and who had T1-2 tumors and 1–3 pathologically positive lymph nodes. The status of radiation therapy, ethnicity, tumor grade, TNM stage, year of diagnosis, number of LNs sampled, number of LNs positive, and estrogen/progesterone receptor status was recorded. Patients missing pathologic or treatment-related information were excluded. Statistical analysis for CSS and OS was performed using the Kaplan-Meier method and analyzed using the log-rank test. Multivariable analysis was performed using the Cox proportional hazards regression model. Statistical analyses were performed using PASW, version 18. Results: 10,517 patients were identified, with a median follow-up of 21.8 months (range 0–47 months). 2339 patients (22.2%) received PMRT. Younger patients, increasing tumor size, increasing tumor grade, and ER negative tumors were more likely to receive PMRT. PMRT was associated with improved OS, 92.8% (95% CI 91.294.4%) versus 88.7% (95% CI 87.7−89.7%), p < 0.001. However, there was no overall CSS benefit to PMRT, p = 0.197. In the subgroup with ER positive tumors, PMRT was associated with both improved OS, 95.5% (95% CI 93.9−97.1%) versus 91.0% (95% CI 90.0−92.0%), p < 0.001, and improved CSS, 97.6% (95% CI 96.6−98.8%) versus 96.1% (95% CI 95.3−96.9%), p = 0.009. Multivariate analysis showed that PMRT was significantly associated with improved survival (HR 0.744, p = 0.011); increasing age, tumor grade, ER negative tumors, increasing tumor stage, and increasing positive nodal ratio were associated with increased risk of death. Conclusion: Patients with intermediate risk breast cancer who received PMRT have improved OS compared to those who did not receive PMRT. For patients with ER positive tumors, PMRT also appears to be associated with improved CSS. Greater consideration for post-mastectomy radiation therapy use may be warranted for this patient population. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-13-11.