Postmastectomy radiotherapy for patients with one to three positive lymph nodes: Utilization and benefit.

Abstract

1116 Background: The use of postmastectomy radiotherapy (PMRT) for patients with pT1-2pN1 tumors is controversial and ASCO guidelines indicate that there is insufficient evidence to make recommendation. We hypothesized that the use of PMRT in this patient group was low and has minimal impact on survival. Methods: The study includes 83,742 invasive breast cancer patients from the National Cancer Data Base who underwent mastectomy with pT1-2 and pN1 disease from 1998-2007. Neoadjuvant cases were excluded. We investigated factors related to PMRT use using cross tables and logistic regression. Survival analysis was conducted using Cox models in patients diagnosed from 1998-2002, with a median follow-up of 5.5 years. Results: The proportion of N1 patients undergoing PMRT remained stable from 1998 to 2007, at approximately 20%. PMRT use increased with larger tumor size (15.4% in T1N1 and 24.4% in T2N1), and with increasing positive lymph nodes (14.6%, 23.7%, and 35.2% for patients with one, two, or three positive nodes, respectively). Age was significantly inversely correlated with PMRT use: the proportion of patients receiving PMRT was 31.3% for age <40 years and 8.2% for 80+ years (p<0.001). Asians are more likely to receive PMRT (25.5%), compared to other races (20.3% white, 20.7% black, and 20.6% Hispanic; p<0.001). PMRT also varied considerably by facility location, the highest in the Northeast at 31.3%, and the lowest in the South at 15.8% (p<0.001). There was only minor difference in PMRT use between different types of cancer centers. Insurance status, income and education level were not associated with PMRT use. After adjusting for prognostic factors in the Cox models, PMRT use was associated with a reduced mortality (hazard ratio=0.87, 95% CI: 0.81-0.93; p<0.001). The multivariable-adjusted 5-year death rate was 16.1% in patients receiving PMRT and 18.1% in patients not receiving PMRT. For pT1N1 tumors the absolute benefit was 1.3% compared to 2.7% for pT2N1 tumors. Conclusions: PMRT use varies with facility and clinicopathologic factors, but not socioeconomic factors. The risks of radiation need to be weighed against the 2% absolute survival benefit when deciding on whether to use PMRT for pT1-2N1 patients.