The influence of breast cancer subtype on survival after palliative radiation for osseous metastases

Abstract

Background Among patients with osseous metastases, breast cancer (BC) patients typically have the best prognosis. In the palliative setting, BC is often considered a single disease, but based on receptor status there are four distinct subtypes: luminal A (LA), luminal B (LB), triple negative (TN), and HER2-enriched (HER2). We hypothesize that survival and palliative outcomes following palliative RT for osseous metastases correlate with breast cancer subtype (BCS). Methods We identified 3,895 BC patients with known receptor status who received palliative RT for osseous metastases from 2004-2013 in the National Cancer Database. Kaplan-Meier method with log-rank testing and univariate/multivariate Cox-regression was used to identify survival factors. Incomplete radiation courses, 30-day mortality rate, and percentage remaining life spent receiving RT (PRLSRT) were calculated. Results Subtypes were 54% LA, 33% LB, 8% TN, and 5% HER2 with median survival of 34.1, 28.2, 5.3, and 15.7 months, respectively (p < 0.001). Overall 82% of patients received >= 10 fractions. Although BCS had limited effect on radiation regimens, TN received nearly twice as many single or hypofractionated (<= 5 fractions) treatments, but the overall rate of these fraction schemes was low at 3.7 and 13.7%, respectively. Compared to LA and LB, TN and HER2 patients had worse palliative outcomes; higher rates of incomplete courses at 18.8% and 18.3% versus 12.7%-14.4%; higher 30-day mortality post-radiotherapy at 21.5% and 16.0% versus 6.3%-7.9%, and higher median PRLSRT of 7.7% and 3.7% versus 2.2%-2.4% for LA and LB. On multivariate analysis, BCS was associated with overall survival with TN (HR 3.7), HER2 (HR 1.75), and LB (HR 1.28) fairing worse than LA (p < 0.001). Conclusions BCS correlated with survival and palliative outcome following radiation to osseous metastases. BCS should be considered by physicians when planning palliative RT to maximize quality-of-life, avoid unnecessary treatment, and ensure palliative benefits.