Background: Since its approval in 2018, guidelines have recommended pembrolizumab in combination with chemotherapy in untreated patients who have advanced NSCLC cancer that lack targetable mutations. When combined with chemotherapy, pembrolizumab improves progression free survival (PFS) and overall survival. For instance, the addition of pembrolizumab to pemetrexed with cisplatin or carboplatin in untreated patients with advanced non-squamous NSCLC provided 8.8 months of PFS versus 4.9 months in the control group. For those with advanced squamous NSCLC, the addition of pembrolizumab to paclitaxel/nab-paclitaxel with carboplatin provided a 6.4 months PFS advantage versus 4.8 months in the control group. Methods: The sample was obtained from a nationwide database of prior authorization requests. All patients with a diagnosis of metastatic NSCLC that received first line treatment between January 1, 2019 to July 31, 2020 were included in the study. Non-squamous NSCLC patients were stratified into two groups: Control (cisplatin or carboplatin and pemetrexed) or Treatment (cisplatin or carboplatin, pemetrexed, and pembrolizumab). Squamous NSCLC patients were stratified into two groups: Control (carboplatin and paclitaxel or nab-paclitaxel) or Treatment (carboplatin, paclitaxel or nab-paclitaxel, and pembrolizumab). Groups were further stratified by ECOG scores of 0 and 1 vs. 2+. Results: No group differences were found across age, gender, and weight groups (p’s>.05). For non-squamous NSCLC patients with ECOG scores of 0 and 1, those in the treatment group (92.2% n=914) were more likely to have a duration ≥ 90 days (χ2=156.53, p<.001) as compared to the control group (70.4%, n=1,308). For squamous NSCLC patients with ECOG scores of 0 and 1, those in the treatment group (90.4%, n=426) were more likely to have a duration ≥ 90 days (χ2=110.95, p<.001) as compared to the treatment group (62.7%, n=980). Similar results were found for patients with ECOG scores of 2+ and across age, gender, and weight groups. Additional analyses to evaluate the maintenance phase of pembrolizumab and time until treatment failure will be undertaken. Conclusion: The findings indicate that metastatic NSCLC patients on pembrolizumab with chemotherapy are more likely to remain on therapy past 90 days as compared to the control group. This study provides real world data and comparative effectiveness research which compliments previously published clinical trials.