(S026) Postmastectomy Radiation Therapy for T3N0 Breast Cancer: A SEER Analysis

Matthew E. Johnson, MD, Elizabeth A. Handorf, PhD, Jeffrey M. Martin, MD, Shelly B. Hayes, MD; Fox Chase Cancer Center

Purpose and Objectives: There is conflicting evidence regarding the benefit of postmastectomy radiation therapy (PMRT) for pathologic stage T3N0M0 breast cancers. We performed a Surveillance, Epidemiology, and End Results (SEER) analysis to investigate the benefit of PMRT in these patients.

Materials and Methods: We queried the SEER database to identify T3N0M0 breast cancer patients diagnosed between 2000 and 2010 who underwent modified radical mastectomy. We excluded metastatic patients, males, and patients in whom the radiation timing or type of radiation was unknown. Our query identified 3,102 patients who we included in this analysis. Statistical analysis was performed utilizing the log-rank test and a Cox proportional hazards model. The primary endpoints were overall survival (OS) and breast cancer-specific survival (CSS).

Results: Of the 3,012 patients identified, 1,226 received PMRT; 74% were Caucasian, 18% were African American, and 8% were Asian or Pacific Islander. The median follow-up was 52 months (range: 0–131 mo). The median number of axillary lymph nodes removed was 11 (range: 0–50). The primary was left-sided in 50.7% of cases. Patients who received PMRT were younger; were more likely to be married; more commonly had higher-grade, estrogen receptor positive (ER+), and progesterone receptor positive (PR+) tumors; and had a different geographic distribution compared with those who did not receive PMRT. There were no differences between the groups in terms of the number of nodes removed or the year of diagnosis.

Several disease and patient characteristics were included in the univariate and multivariate analyses, including year of diagnosis, age, grade, race, ER status, PR status, primary quadrant location, number of nodes examined, education, income, histology, and use of PMRT. On univariate analysis, the use of PMRT improved OS (76.1% vs 58.8%; P < .01) and CSS (84.7% vs 80.1%; P < .01) at 8 years. After controlling for all the variables listed above, the use of PMRT remained significant on multivariate analysis: patients who received PMRT had improved OS (hazard ratio [HR] = 0.60; P < .01) and CSS (HR = 0.75; P = .01) compared with those who did not receive PMRT. Grade also predicted for improved CSS on multivariate analysis (P < .01).

A subgroup analysis examining the impact of grade demonstrated that PMRT improved CSS only for high-grade tumors but not for low-grade tumors. For high-grade (III–IV) tumors, CSS at 96 months was 80.4% for PMRT vs 74.1% in the unirradiated group (P = .01). For low-grade (I–II) tumors, CSS at 96 months was 89.3% for PMRT vs 87.6% without PMRT (P = .09).

Conclusion: PMRT was associated with significant improvements in both CSS and OS in patients with T3N0M0 breast cancers treated with modified radical mastectomy from 2000 to 2010. PMRT should be strongly considered in these patients, especially those with high-grade tumors.

Proceedings of the 96th Annual Meeting of the American Radium Society - americanradiumsociety.org