Prognosis and predictors of site of first metastasis after definitive radiation therapy for non-small cell lung cancer.

Background and purpose Evidence suggests that distinct biologic phenomenon produce different patterns of distant metastatic (DM) failures. We attempted to identify prognostically poor sites of first DM and to define factors predictive of their development. Methods and materials A total of 1074 patients treated with ≥60 Gy definitive radiation for initially non-metastatic non-small cell lung cancer (NSCLC) were analyzed. Uni- and multivariate Cox regression was utilized to associate clinical factors with DM site, and metastatic site with overall survival (OS). To account for competing events, multivariate Fine and Gray regression was utilized to identify treatment and disease factors predictive of site-specific metastases. Results Sites of first DM associated with worse survival were liver (median OS: 5 months after DM) and bone (median OS: 6.7 months after DM). Multivariate regression identified non-squamous histology to be associated with first DM within the liver (HR = 2.04, 95% CI 1.16-3.60, p = 0.01), while delay between diagnosis and RT (third vs. first tertile: HR = 2.3, 95% CI 1.26-4.21, p = 0.007) in addition to advanced stage (stage III vs. II/I: HR = 2.37, 95% CI 1.11-5.06, p = 0.03) were associated with first DM within bone. Conclusions Liver and bone as site of first DM is associated with worse prognosis and are predicted by different disease and treatment factors.