(S043) Heterogeneity in Treatment Response of Spine Metastases to Spine Stereotactic Radiosurgery Within “Radiosensitive” Subtypes

Abstract

To characterize outcomes of metastatic colorectal and non-small cell lung cancer (NSCLC) histologies, compared to other radiosensitive histologies, treated with spine stereotactic radiosurgery (SSRS) with regards to local control, overall survival, and predictors of response. A total of 136 patients with 161 SSRS treated metastatic lesions at our institution between 2003 and 2016 were reviewed. We assessed clinical endpoints in relation to histological type including local control (LC) and overall survival (OS) using univariate and multivariate analyses. For all patients, the 1 and 2 year actuarial rates for LC were 82.3% and 75.2%; and rates for OS were 72.5% and 52.8% respectively. Among tumor histologies, 1 year LC rates for thyroid, breast, lung, colon, and other cancers were 90.7%, 93.5%, 70.7%, 60.4% and 82.5%. When analyzed together, NSCLC and colorectal cancers had significantly poorer local failure free survival rates at 1 and 2 years (67.5% and 58.4%, respectively), than all other histologies (90.4% and 84.0%% respectively, p=0.0004). NSCLC/colorectal tumor status was a significant predictor of local failure on COX univariate (HR 2.71, 95% CI 1.38 – 5.33, p = 0.004) and multivariate (HR 3.14, 95% CI 1.57 – 6.29, p = 0.001) analysis, as well as a significant variable in a competing risk multivariate model (HR 2.07 95% CI 1.08 – 3.97, p = 0.029) when compared to other tumor types. SSRS is a safe and effective strategy in achieving local control of spine metastases, particularly among radiosensitive histologies. However, a subset of these classically defined histologies (NSCLC and colorectal) has a propensity towards local failure. In addition to resulting in poorer OS outcomes, the poor LC rates seen in NSCLC and colorectal cancers in this study are more consistent with a radioresistant phenotype suggesting the need for optimized dosing regimens in this subgroup.