LAUSR

141 Background: Dabrafenib plus trametinib (D+T), ipilimumab plus nivolumab (I+N), and both nivolumab and pembrolizumab (“PD-1 mono”) are approved for the 1L treatment of MM. This study reports real world 1L TTNT for patients receiving these therapies by LDH status. Methods: This was a retrospective, observational study. MM patients initiating 1L treatment with D+T, I+N, or PD-1 monotherapy from Jan-2014 through Jun-2017 were identified from community oncology practices in the U.S. Patients treating oncologist abstracted patient date into case report forms. LDH at initiation of treatment was classified by the provider as normal or abnormal ( > 1x and < 2x ULN or ≥ 2x ULN) according to the reference laboratory. TTNT was calculated from 1L initiation to initiation of second-line (2L). Cox proportional hazard models estimated the risk of initiating 2L (proxy for progression) between groups adjusted for age, gender, brain/liver metastases (mets), number of mets and ECOG-PS. Results: Data for 332 patients were submitted by 53 providers including 51.6% who initiated 2L. Abnormal LDH: D+T = 60.3%, ipi/nivo = 53.0%, PD-1 mono = 35.4%. No differences in the frequency of patients with stage IV M1c, brain mets, ECOG, or discontinuation due to toxicity (8.4% of all patients) were noted between cohorts. TTNT was significantly longer in both normal and abnormal LDH cohorts for D+T (14.1 and 11.6 mo.) vs. ipi/nivo (10.1 and 10.2 mo.) but not PD-1 mono (13.3 and 10.6). Adjusted for confounding variables in the abnormal LDH cohort the hazard ratio (HR) for risk of 2L initiation was significantly higher (2.08, p < 0.01) for ipi/nivo vs. D+T but not significant different among normal LDH patients (HR = 1.89, p = 0.054). No significant difference in the risk of 2L initiation between D+T and ipi/nivo were noted in either the normal or abnormal cohorts. Conclusions: For normal and abnormal LDH cohorts 1L TTNT was longer for patients receiving D+T vs. ipi/nivo (but not vs. PD-1 mono). Using the multivariate model we observed the risk of 2L initiation, a proxy for progression, was higher for ipi/nivo treated vs. D+T adjusted for clinical factors for abnormal LDH patients.