Time from stereotactic body radiotherapy to immunotherapy as a predictor for outcome in metastatic non small cell lung cancer.

9024 Background: Immunotherapy has changed the face of treatment for stage IV non small cell lung cancer (NSCLC), quickly becoming the standard of care. The appropriate timing of immunotherapy in the setting of other ablative therapies, namely stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT), remains to be determined. We sought to use the National Cancer Database to examine trends in immunotherapy use as well as timing as it relates to SBRT/SRS in stage IV NSCLC patients. Methods: We queried the NCDB for patients with Stage IV NSCLC diagnosed between 2004-2015 that were treated with SRS or SBRT techniques (to any site) and had at least three months of follow up. Multivariable logistic regression was used to identify predictors of immunotherapy use. Receiver operator curve analysis was used to identify the optimal timepoint between SBRT and immunotherapy correlating with overall survival. Kaplan-meier curves were generated to determine overall survival. Multivariable cox regression was used to determine factors predictive of survival. A propensity score was generated and incorporated into Kaplan-meier and cox regressions to account for indication bias. Results: We identified 13,862 patients meeting the above eligibility criteria, 371 being treated with immunotherapy. The vast majority (75%) had chemotherapy as well. Patients with adenocarcinoma, treatment with chemotherapy, and more recent year of treatment were more likely to receive immunotherapy. Univariable Kaplan-meier analysis showed improved median survival with immunotherapy, 17 months vs. 13 months, p < 0.0001. On multivariable propensity-adjusted cox regression significant predictors for improved overall survival were younger age, lower comorbidity score, lower grade, private insurance, and female gender. Using a cutoff of 21 days after start of SBRT, patients treated thereafter were more likely to survive longer, median survival of 19 months vs 15 months, p = 0.0335. Conclusions: Immunotherapy use in Stage IV NSCLC after SBRT has increased over time, mostly in patients with adenocarcinoma and in the setting of chemotherapy. In this analysis, outcomes were improved when immunotherapy was given at least three weeks after start of SBRT.