Background: In CheckMate 141, nivo resulted in significantly prolonged overall survival (OS), favorable safety, and stable quality of life vs IC in patients (pts) with platinum-refractory (PR) R/M SCCHN. Cetuximab, a formal trial stratification factor, permits exploratory subgroup assessment. Outcomes by prior cetuximab use are described. Methods: CheckMate 141 was a randomized, open-label, phase 3 trial (NCT02105636) in which pts (N = 361) with PR R/M SCCHN were randomized 2:1 and stratified by prior cetuximab use to nivo 3 mg/kg every 2 weeks or IC of methotrexate, docetaxel, or cetuximab. The primary endpoint was OS; additional endpoints were progression-free survival (PFS), objective response rate (ORR), and safety. A multivariate analysis will explore influence of additional factors. Results: Nivo improved OS vs IC regardless of prior cetuximab, and improvement was greater in pts without prior cetuximab (Table). Median OS was longer for nivo vs IC in pts with PD-L1 expression ≥ 1% regardless of prior cetuximab, and in pts with PD-L1 expression < 1% without prior cetuximab. Among pts with PD-L1 expression ≥ 1%, ORR was higher with nivo vs IC with/without prior cetuximab. PFS was similar regardless of prior cetuximab. Grade 3–4 treatment-related adverse event rates for nivo vs IC were 11.7% vs 40.9% with prior cetuximab and 15.4% vs 26.7% without prior cetuximab. Conclusions: OS and ORR improved with nivo vs IC regardless of prior cetuximab use, and the magnitude of benefit was greater in pts without prior cetuximab exposure. These results support the use of nivo for R/M SCCHN regardless of prior cetuximab use. Clinical trial information: NCT02105636

HPV = human papillomavirus; HR = hazard ratio; PD-L1 = programmed death ligand 1