Background: Tyrosine Kinase inhibitors (TKI) have changed the treatment paradigm in patients with stage IV adenocarcinoma of the lung (AdenoCa) harboring epidermal growth factor receptor (EGFR) mutation. Currently there are no guidelines for reflex pathologic testing or mandatory reporting of these mutations. Methods: Data for age, sex, race/ethnicity, SES, diagnosis year and EGFR mutation status (+/-) in Stage IV lung AdenoCa (2005-2015) were extracted from the population-based California Cancer Registry (CCR). Logistic regression assessed the proportion of AdenoCa patients that received EGFR testing by age, socioeconomic status quintile (SES), gender and race/ethnicity. Proportional hazards analysis evaluated survival by EGFR status. Among EGFR positive patients, demographic factor adjusted, lung cancer specific Cox proportional mortality hazards ratios (HR) were compared for use of TKI (Y/N). Results: Of the 23,674 patients, 3,916 (17%) had EGFR results in their report; this percentage increased for ordinally higher SES quintiles (Trend p < 0.001). Odds of EGFR testing (Y/N) increased from 2005 to 2015 (p < 0.001) and the odds ratio was higher for females vs. males (OR = 1.20;95%CI = 1.11-1.30;p < 0.001). Odds of EGFR testing was higher for Asian/Other and lower for non-Hispanic black patients vs. non-Hispanic white (OR = 1.32;95%CI = 1.20-1.45;p < 0.001 and OR = 0.86;95%CI = 0.74-0.99;p = 0.002), respectively. Among EGFR tested patients, 1,173 (30%) were positive, 2,618 (67%) negative and 125 (3%) had unknown status. Median survival time was 858 days and 390 days for TKI (Y/N). Adjusted HR for TKI (Y/N) was 0.61; 95%CI = 0.58-0.64; p < 0.001). Conclusions: These findings reveal that, in spite of EGFR testing recommendations, only about 17% of patients had evidence of testing. The trend for higher testing prevalence in higher SES quintiles and during recent years is consistent with more comprehensive insurance and improving compliance. These findings reveal remarkably increased survival for EGFR positive patients treated with TKI. These findings underscore the need for reflex pathologic testing for EGFR mutations in advanced lung AdenoCa to improve patient outcomes and avoid delays in treatment.