Background: Recent real-world studies observed that some aNSCLC pts with ADO initiated non-targeted therapy (non-TT) before biomarker test results became available. This study assesses the clinical impact of the timing of first line (1L) TT in aNSCLC pts with ADO. Methods: In a retrospective analysis of the nationwide Flatiron Health electronic health record-derived de-identified database, pts aged ≥18 years, diagnosed (Dx) with aNSCLC between 1/1/2015-10/18/2022, had ADO (ALK, BRAF, EGFR, RET, MET, ROS-1, or NTRK) based on biomarker testing ≤ 90 days of advanced Dx, and received 1L treatment (tx) were included. Cohorts were defined by tx patterns after test result: Cohort 1 received 1L TT ≤ 42 days; Cohort 2 initiated 1L non-TT before or after testing but switched to TT ≤ 42 days; Cohort 3 initiated non-TT before or after testing and did not switch to TT ≤ 42 days. Pts were followed from test results + 42 days until 11/30/2022 or death, whichever earliest. Multivariate Cox regression evaluated real-world progression-free survival (rwPFS) and overall survival (OS) between cohorts. Results: A total of 5156 aNSCLC pts with ADO were included: 79% were treated in the community setting and 56% received NGS testing. Most common ADO were EGFR and ALK for both Cohort 1 (78% and 13%) and Cohort 2 (67% and 24%); EGFR (39%) and BRAF (35%) for Cohort 3. Cohort 3 included more rare mutations (MET, NTRK, RET). Statistically significant differences were observed in gender, race/ethnicity, practice type, and area-level socioeconomic status across all cohorts. There was no significant difference in outcomes observed between Cohort 2 and 1, but significantly inferior outcomes in Cohort 3 vs 1. Conclusions: Our findings demonstrated better outcomes with upfront 1L TT vs non-TT in aNSCLC pts with ADO. The comparable outcomes between pts who received 1L TT after test result and pts who switched to TT ≤ 42 days of test result available underscore the importance of timely tx decisions based on ADO detection in lieu of tx-switch at progression. Opportunities remain to improve utilization of NGS to identify all ADO upfront to inform the appropriate 1L TT when indicated.