BACKGROUND: FOLFIRINOX (FFX) and gemcitabine plus nab-paclitaxel (GN) are established first line therapies for metastatic pancreatic cancer (MPC). There are, however, no randomized controlled trials comparing FFX and GN in the first line setting and real-world data on their comparative effectiveness is limited. We aimed to evaluate the outcomes of patients with MPC who were treated with first line FFX and GN and to further characterize dose modifications, discontinuation rates due to treatment toxicity, and rates of hospitalizations while on treatment. METHODS: We manually abstracted data from the electronic medical records (EMR) system at Yale Smilow Hospital and Smilow Cancer Hospital Care Centers for patients with MPC treated with at least one cycle of first line FFX or GN from January 2011 to April 2019. Patients who received prior neoadjuvant or adjuvant FFX or GN and adjuvant gemcitabine less than 6 months prior to metastatic recurrence were excluded. The median time to treatment discontinuation (TTD) and overall survival (OS) were determined using Kaplan-Meier method. RESULTS: We identified 363 patients for analysis; 269 (74%) patients were treated with FFX and 94 (26%) with GN. Median TTD was 4.8 (IQR, 2.3-8.0) months in the FFX group compared to 3.4 (IQR, 1.3-5.7) months in the GN group (P=0.0037). Median OS was 11.3 (95% CI: 10.7-12.9) months in the FFX group and 7.0 (95% CI: 6.0-8.7) months in the GN group (P<0.001). Initial dose modifications occurred in 264 (98%) and 86 (91%) of FFX and GN treated patients, respectively (P=0.001). While on treatment, 56 (60%) of GN-treated patients had at least one hospitalization vs. 110 (41%) in the FFX-group (P=0.002). Treatment was discontinued due to chemotherapy toxicity in 26 (10%) and 14 (15%) among the FFX and GN cohorts, respectively (P=0.275). CONCLUSIONS: Patients treated with first line FFX had increased survival and TTD compared to patients treated with GN despite increased dose modifications and similar rates of treatment discontinuation due to treatment-related toxicity. GN-treated patients were older and more likely to be hospitalized while on treatment. Further study evaluating comparative effectiveness between these two regimens is warranted.