Immune Checkpoint Inhibitors Improve Survival and Local Control in Patients With Spine Metastasis After Stereotactic Body Radiotherapy

Purpose/Objective(s) Radiotherapy, especially high-dose radiation in the form of stereotactic body radiotherapy (SBRT), may stimulate the therapeutic effect of immune checkpoint inhibitors (ICIs). Both SBRT and ICIs play an increasingly important role in the management of spine metastasis. We hypothesize that SBRT and ICI may act synergistically to improve the outcomes of patients with spine metastasis. Materials/Methods We retrospectively reviewed patients with spine metastasis treated with SBRT at an academic center between 2009 and 2019. Patients who received ICI at any point during their disease course were compared to those with the same primary tumor types who did not receive ICI. Cox proportional hazard analyses were performed for overall survival (OS) and local control (LC), adjusting for primary tumor type, age, performance status, and prior spine surgery and/or radiation. Results 153 patients with 194 unique spine lesions were treated with SBRT. The most common primary tumor types were renal cell carcinoma (RCC), non-small cell lung cancer (N = 48, 31% each), colorectal cancer (N = 21, 14%), melanoma and liver cancer (N = 10, 6% each). 82 patients received at least one course of ICI. The most common type of ICI was single-agent anti-PD-1 (N = 71, 88%), followed by dual anti-CTLA-4/PD-1 inhibitors (N = 14, 17%). Of patients receiving ICI, 44 (53.6%) initiated ICI before SBRT, and 38 (46.4%) received ICI after SBRT. The median survival (MS) after SBRT was 14.8 months (95% confidence interval [CI] 11.4-19.6). On univariable analysis, MS was significantly longer for patients starting ICI after SBRT (27.3 months, 95% CI 16.0-33.9) than for those who did not receive any ICI (MS 11.3 months, 95% CI 8.9-15.8, P = 0.04). Patients with RCC (HR 0.67, 95% CI 0.45-1.00, P = 0.05) and higher body mass index (BMI, HR 0.97 as continuous variable, 95% CI 0.93-1.00, P = 0.05) trended toward longer OS. On multivariable analysis after adjusting for primary tumor type, performance status and BMI, only ICI treatment after SBRT was significantly associated with increased survival (HR 0.62, 95% CI 0.39-0.98, P = 0.04). LC after SBRT was numerically higher in patients receiving ICI (1-year LC 91.3%, 95% CI 82.4-95.8%; 2-year 79.7%, 95% CI 65.7-88.5%), than those who did not (1-year 81.5%, 95% CI 65.9-90.5%; 2-year LC 55.5%, 95% CI 35.6-71.4%), although this was not statistically significant (P = 0.18). ICI Initiation before SBRT trended toward superior LC compared to no ICI (multivariable HR 0.49, 95% CI 0.22-1.08, P = 0.08). Both epidural disease and paraspinal extension were associated with worse LC on univariable and multivariable analyses. Conclusion ICIs may enhance survival and tumor control after SBRT for patients with spine metastasis. Post-SBRT ICI may improve systemic disease control and survival, while pre-SBRT ICI may augment LC. Further research is needed to maximize the synergy between these two treatment modalities. Author Disclosure X. Chen: None. M.C. LeCompte: None. L.R. Kleinberg: Research Grant; Novartis, Novocure, Accuray, Arbor. Honoraria; Accuray. Advisory Board; Novocure. Travel Expenses; Accuray. R.K. Hales: Research Grant; Genentech. K. Voong: Research Grant; Radiation Oncology Institute, Lung Cancer Research Foundation, Canon, Inc. P. Forde: Research Grant; Bristol Myers-Squibb, AstraZeneca, Kyowa-Kirin, Novartis. Honoraria; Bristol Myers-Squibb, AstraZeneca, Novartis, Merck, AbbVie, EMD, Inivata. J.R. Brahmer: Research Grant; AstraZeneca, Bristol Myers Squibb, Genentech/Roche, Merck, RAPT Therapeutics, Revolution Medicines. Consultant; Amgen, Bristol Myers Squibb, Genentech, Eli Lilly, GlaxoSmithKline, Merck, Sanofi. M. Markowski: Honoraria; Clovis Oncology, Exelixis. D.M. Ryan II: None. L. Lo: None. D.M. Sciubba: Consultant; Medtronic, DePuy-Synthes, Baxter. K.J. Redmond: Research Grant; Elekta AB, Accuray. Honoraria; AstraZeneca, Accuray. Travel Expenses; Elekta AB, Accuray.