Breast Cancer

PV 01 - Poster Viewing Q&A - Session 1

SU_4_2033 - Outcomes After Post-Mastectomy Radiation for Pathologic Stage I or II Triple Negative Breast Cancer: A NCDB Analysis

Sunday, September 15
1:15 PM - 2:30 PM
Location: ASTRO Innovation Hub

Outcomes After Post-Mastectomy Radiation for Pathologic Stage I or II Triple Negative Breast Cancer: A NCDB Analysis
N. Agrawal1, J. A. Holmes1, N. Ohri2, R. C. Zellars1, and R. M. Rhome1; 1Indiana University Department of Radiation Oncology, Indianapolis, IN, 2Rutgers Cancer Institute of New Jersey, New Brunswick, NJ

Purpose/Objective(s): Triple negative breast cancer (TNBC) accounts for 15-20% of all breast cancers. Current post-mastectomy radiation treatment (PMRT) guidelines for early stage TNBC are based on clinical trials that included all histologic subtypes, though TNBC is considered at higher recurrence risk. Some studies suggest that PMRT in early (Stage I-II) TNBC improves overall survival (OS). The purpose of this study was to utilize the National Cancer Database (NCDB) to determine if PMRT in this cohort treated in the United States is associated with OS.

Materials/Methods: Using NCDB, we identified 13,618 patients diagnosed between 2010-2015 with pathologic stage T1-T2, N0-N1, triple negative histology, who underwent mastectomy and adjuvant multi-agent chemotherapy. Patients before 2010 did not have Her2 status encoded. PMRT was defined as receipt of radiation to the chest wall/nodes to 40-60Gy. Cox proportional hazards multivariate regression analysis was performed to compare overall survival by PMRT group, adjusting for T-stage, N-stage, age, margin, grade, lymphovascular invasion (LVI), insurance status, treatment at academic center, race, and comorbidity score.

Results: PMRT was given to 2,461 patients (18.2%) and the remaining 11,065 (81.8%) had no radiation. The median age of the cohort was 53. 6,393 (48.7%) of patients had T1 disease and 10,033 (73.9%) had N0 disease. Hazard ratio (HR) of death for PMRT, adjusted for the above factors, was 1.02 (95% confidence interval [CI] 0.88-1.18, p=0.76). Factors that were associated with lower OS were older age (HR=1.22, 1.07-1.40, p=0.003), LVI (HR=1.50, 1.31-1.71, p<0.001), higher T stage (HR=1.58, 1.39-1.81, p<0.001), higher N stage (HR=1.52, 1.31-1.76, p<0.001) and higher comorbidity score (1.34, 1.16-1.55, p<0.001), while treatment at an academic center (HR=0.84, 0.74-0.95, p<0.006), private insurance (HR= 0.72, 0.51-0.99, p=0.049) and Asian race (0.62, 0.45-0.88, p=0.006) were associated with improved overall survival.

Conclusion: Receipt of PMRT for T1-2N0-1 triple negative patients who underwent mastectomy and adjuvant multi-agent chemotherapy was not associated with differences in overall survival in this cohort. Due to the heterogeneity of TNBC, further studies need to be conducted in a patient population representative of the United States to determine if a subgroup of early stage TNBC patients has overall survival benefit with the addition of PMRT.

Author Disclosure: N. Agrawal: None. J.A. Holmes: None. N. Ohri: None. R. Zellars: Board Member; Indiana University Health Physicians.

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