Background: Current national guidelines recommend epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) as first-line (1L) for EGFR mutated metastatic non-small cell lung cancer (EGFRm mNSCLC) patients. Depending on the aggressiveness of the tumor, physicians may initiate immunotherapy (IO) alone or in combination with chemotherapy (IO± chemo) or chemotherapy alone prior to receiving biomarker test results. Objective: To evaluate timing of 1L therapy in relation to biomarker test results and time to next treatment (TTNT) in EGFRm mNSCLC patients receiving EGFR TKIs versus other 1L therapies. Methods: Adults with EGFRm mNSCLC who initiated 1L EGFR TKI, IO ± chemo, or chemotherapy alone, from 5/2017-12/2019 were identified from Flatiron Electronic Health Record-derived database. Logistic regression was used to generate adjusted odds ratio (OR) and 95% confidence intervals (CI) for receipt of specific 1L therapy based on timing of EGFR testing results. Kaplan-Meier analysis was used to evaluate the median TTNT as a proxy for progression-free survival. Adjusted hazard ratios (HR) and 95% CI representing the effect of 1L therapy on TTNT were reported from multivariable Cox proportional-hazards models. Results: Among 758 EGFRm patients, EGFR TKI was used as 1L therapy for 87.3% of patients (n=662), IO± chemo in 8.3% (n=63), and chemotherapy only in 4.4% (n=33). The majority of IO ± chemo (61.9%) and chemotherapy only patients (60.6%) initiated therapy before test results were available, compared to 9.7% of EGFR TKIs. The odds of receiving an EGFR TKI were higher compared to both IO ± chemo (OR: 19.6, p<0.001) and chemotherapy (OR: 14.1, p<0.001) when therapy was initiated after test results were available. Compared to IO ± chemo and chemotherapy alone, EGFR TKIs had a longer median TTNT (EGFR TKI: 14.8 months, 95% CI: 13.5-16.3; IO ± chemo: 3.7 months, 95% CI 2.8-6.2; chemotherapy: 4.4 months, 95% CI 3.1-6.8, p<0.001). Adjusting for demographic and clinical characteristics showed that EGFR TKI patients had significantly lower risk of initiating second-line therapy or death compared to patients on 1L IO ± chemo (HR: 0.33, p<0.001) or 1L chemotherapy (HR: 0.34, p<0.001). Conclusions: Patients in which treatment was initiated after testing results were available were much more likely to initiate guideline recommended EGFR TKI therapy. EGFR TKIs were associated with longer TTNT than IO ± chemo or chemotherapy.