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

Purpose To characterize outcomes of metastatic colorectal and non-small cell lung cancer (NSCLC) histologies, compared with other radiosensitive histologies, treated with spine stereotactic radiosurgery with regard to local control, overall survival, and predictors of response. Methods and Materials A total of 127 patients with 148 spine stereotactic radiosurgery–treated metastatic lesions at our institution between 2003 and 2013 were reviewed. We assessed clinical endpoints in relation to histologic type, including local control (LC) and overall survival (OS), using univariate and multivariate analyses. Results For all patients, the 1- and 2-year actuarial rates for LC were 82.6% and 75.8%, and rates for OS were 72.9% and 51.5% respectively. Among tumor histologies, 1-year cumulative incidence rates of local failure for thyroid, breast, lung, and colon cancer were 8.7%, 7.0%, 26.6%, and 39.6%, respectively. When analyzed together, NSCLC and colorectal cancers had significantly greater cumulative incidence rates at 1 and 2 years (30.4% and 38.7%, respectively) than other histologies (8.0% and 14.1% respectively, P=.0008). Non-small cell lung cancer/colorectal tumor status was a significant predictor of local failure in a competing risk univariate model (hazard ratio 2.12, 95% confidence interval 1.07-4.17, P=.03) and multivariate model (hazard ratio 2.35, 95% confidence interval 1.12-4.92, P=.024). Conclusions Spine stereotactic radiosurgery is an 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 toward 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.