Patient-reported outcomes (PROs) in the C-POST trial of adjuvant cemiplimab (cemi) vs placebo (pbo) for high-risk cutaneous squamous cell carcinoma (CSCC).

6065 Background: C-POST is a phase 3, double-blind, pbo-controlled trial (NCT03969004) of adjuvant cemi for treatment of patients (pts) with CSCC at high risk of recurrence after surgery and radiation therapy. Positive results for the primary endpoint of disease-free survival (DFS) at interim analysis 1 are reported in a separate ASCO abstract. Here we evaluate adjuvant cemi vs pbo on PROs as exploratory endpoints. Methods: Pts (N=415) were randomized 1:1 to adjuvant cemi or pbo for up to 48 weeks (4 cycles). The European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire Core 30 (QLQ-C30) was administered at Day 1 of every cycle, end of treatment, and during follow-up. The pre-specified PRO analysis focused on 6 QLQ-C30 scales of global health status (GHS)/QoL; 3 functional scales (physical [PF], role [RF], emotional [EF]); and 2 symptom scales (fatigue [FA], pain [PA]). Overall changes from baseline across treatment cycles were analyzed using mixed effects models for repeated measures; if 95% CIs did not cross zero, differences were considered of nominal statistical significance (α=0.05) as no adjustment was made for multiplicity. PRO responder analysis used a published threshold of 10 points for clinically meaningful change across scales; median time to first deterioration was determined using Kaplan–Meier analyses. Results: QLQ-C30 completion rates from baseline through all cycles were >88% in both arms. Baseline scores showed moderate-to-high GHS/QoL and functioning and low symptom burden (Table). Overall changes from baseline on QLQ-C30 GHS/QoL, functioning, and symptom scores were small and similar between arms (Table). In the PRO responder analysis, most pts in both arms reported maintenance or clinically meaningful improvement in QoL in all scales across all cycles (cemi: 55.9–86.8%; pbo: 55.5–88.2%). Median time to first deterioration was also similar between arms in all scales (cemi: 5.3–25.6 months; pbo: 8.3–22.2 months). Conclusions: QoL was maintained during treatment with adjuvant cemi, with no clinically meaningful worsening vs pbo. These PRO results complement the observed improvement in DFS and support the favorable risk profile of adjuvant cemi for pts with high-risk CSCC. Clinical trial information: NCT03969004 . QLQ-C30 scale Baselinemean (SD) Overall LS mean change from baseline (95% CI) Difference (95% CI) Cemi (n=209) Pbo(n=206) Cemi(n=209) Pbo(n=206) GHS/QoL 75.4 (17.5) 75.8 (17.4) –2.0 (–4.3, 0.4) –1.0 (–3.4, 1.4) –0.9 (–3.7, 1.8) PF 87.1 (16.0) 90.6 (13.9) –1.4 (–3.2, 0.5) –1.9 (–3.9, 0.0) 0.5 (–1.7, 2.7) RF 83.8 (24.8) 84.2 (20.8) –4.2 (–7.3, –1.2) –1.6 (–4.8, 1.5) –2.6 (–6.2, 0.9) EF 84.6 (18.7) 85.1 (16.7) 0.2 (–2.2, 2.7) –0.4 (–2.9, 2.1) 0.7 (–2.2, 3.5) FA 20.9 (19.9) 20.5 (20.1) 5.0 (2.2, 7.7) 4.2 (1.4, 7.0) 0.8 (–2.4, 4.0) PA 14.7 (21.2) 13.1 (20.4) 3.2 (–0.1, 6.5) 2.1 (–1.3, 5.6) 1.1 (–2.8, 5.0)