e20646 Background: Epidermal growth factor receptor (EGFR) mutation is a strong predictor of response to EGFR tyrosine kinase inhibitors (TKI). However, response duration is variable. The predictive value of EGFR mutation for response is superior to previously reported clinical predictors, namely female gender, Asian ethnicity, smoking status, and histology. It is unclear, however, whether any clinical characteristics have additive predictive value for duration of response to EGFR-TKI. Here, we attempted to identify clinical predictors of response duration to EGFR-TKI in EGFR-mutant NSCLC. Methods: Review of a prospectively collected lung cancer patients’ database at a tertiary care hospital was performed. Stage IV EGFR-mutant patients diagnosed between 2004 and 2015 who received EGFR-TKI for ≥ 3 months, at any line of treatment, were included. The following variables were collected for purpose of analysis: age, gender, smoking status, tumor histology, specific EGFR mutation (exon 19 versus 21 mutation), ECOG PS, line of TKI treatment, and serum CRP levels. Chi square and t-test were used where appropriate. Univariate and mutivariate modeling was used to explore the predictive power of covariates. Results: One hundred ten patients with EGFR mutant stage IV lung cancer were included in this study. Patients were predominantly female (77%), never or light smokers (57%), with non-squamous histology (93%) and an exon 19 mutation (66%). Mean duration of treatment with EGFR-TKI was 14.4 (range 3-86) months. In univariate analysis, never-smoking status, exon 19 mutation and low serum CRP were predictive of a longer EGFR-TKI treatment duration. However, in multivariate analysis only exon 19 and CRP level were significantly associated with longer duration of response to EGFR-TKI. Conclusions: Gender, smoking status and ethnicity- although initially identified as predictors of response to EGFR-TKI in an unselected population- do not confer additional predictive potential of treatment response duration in EGFR mutant NSCLC patients. Only serum CRP level- and exon 19 mutation status- are independently associated with duration of response to EGFR-TKI in this population.