Overall survival benefit from tebentafusp in patients with best response of progressive disease.
Authors: Joshua Anthony M. , Baurain Jean-Francois , Piperno-Neumann Sophie , Nathan Paul , Hassel Jessica Cecile , Butler Marcus O. , Schlaak Max , Sullivan Ryan , Ochsenreither Sebastian , Dummer Reinhard , Kirkwood John M. , Sacco Joseph J. , Shoushtari Alexander Noor , Orloff Marlana , Piulats Josep M. , Abdullah Shaad Essa , Deo Mughda , Lockwood Sarah , Rutkowski Piotr 
Published: June 2021

9509 Background: Tebentafusp (tebe) is the first T cell receptor (TCR) therapeutic to demonstrate an overall survival (OS) benefit in a randomized Phase 3 (Ph3) study [ NCT03070392 ]. In Ph2, 42% of pts with best overall response (BOR) of progressive disease (PD) survived > 1 year (yr), suggesting RECIST-based radiographic assessments underestimate OS benefit of tebe. Here we analyzed OS in the Ph3 study in a cohort of pts with BOR of PD by comparing tebe to the control arm of investigator’s choice (IC). Methods: 378 pts were randomized in a 2:1 ratio to tebe vs. IC. BOR was assessed by investigators using RECIST v1.1. Treatment beyond first disease progression (TBP) was permitted for both arms. On the IC arm, only patients receiving pembrolizumab (pembro) continued with TBP and were included in the TBP-related analyses. No crossover to tebe was permitted; investigators were free to choose subsequent therapy. This analysis was conducted on the first interim analysis (data extracted Nov-2020). Kaplan-Meier estimates of OS were based on Day 100 landmark to eliminate immortal time bias and to capture majority of the PDs. Results: By Day 100, PD as BOR occurred in 52% (130/252) of tebe pts (PD-tebe) vs. 60% (76/126) of IC pts (PD-IC). Key baseline characteristics including lactate dehydrogenase, alkaline phosphatase, ECOG performance, age, and sex were similar between PD-tebe vs PD-IC. The proportion of pts with PD due to progression of target lesions (TL), non-TL, or new lesions were also similar between the two groups. More pts received TBP among PD-tebe 53% (69/130) vs PD-pembro 16% (10/61). Median duration of TBP was longer for PD-tebe (7 weeks) vs PD-Pembro (3 weeks). The safety profile of PD-tebe pts during TBP was similar to all tebe-treated pts. OS was superior for PD-tebe vs PD-IC, HR = 0.41 (95%CI 0.25-0.66), even when considering key baseline covariates. While some pts had regression of TL despite diagnosis of PD ( < 10% of pts), the OS benefit remained even when limited to pts with best change of tumor growth of TL, HR 0.46 (0.29, 0.73). 58% (75/130) PD-tebe and 52% (40/76) PD-IC pts received subsequent therapies. In a landmark OS analysis of these pts beginning on 1st day of subsequent therapy, prior tebe was associated with better OS vs. prior IC, HR 0.59 (95%CI 0.36-0.96). Conclusions: Tebe is the first TCR therapeutic to demonstrate an OS benefit in a solid tumor. Surprisingly, a strong OS benefit from tebe is observed even in pts with BOR of PD, suggesting that RECIST-based radiographic assessments do not capture the complete benefit from tebe. The safety profile of tebe during TBP was consistent with that for long-term tebe treatment. Clinical trial information: NCT03070392.