1318PPhase II study of 2 dosing regimens of cemiplimab, a human monoclonal anti–PD-1, in metastatic cutaneous squamous cell carcinoma (mCSCC)

Abstract Background Cemiplimab-rwlc is the only US FDA-approved treatment for patients (pts) with advanced CSCC. The primary analysis of a weight-based regimen of cemiplimab 3 mg/kg IV dosed every 2 weeks (Q2W) in mCSCC has been published; follow-up data are reported here. The primary analysis for the approved fixed-dosing regimen of cemiplimab 350 mg IV dosed every 3 weeks (Q3W) in mCSCC, which displays comparable pharmacokinetics to weight-based dosing, is also reported. Methods In a phase II study (NCT02760498), pts with mCSCC received IV cemiplimab as a weight-based regimen for up to 96 weeks (Group [Gp] 1, n = 59) or a fixed regimen for up to 54 weeks (Gp 3, n = 56). The primary objective was objective response rate (ORR) per independent central review (ICR; RECIST 1.1 for scans, modified WHO criteria for photos). Results Baseline characteristics were similar in both gps (Table). Median (range) duration of follow-up was 16.5 (1.1–26.6) months (mos) for the Gp 1 update and 8.1 (0.6–14.1) mos for the Gp 3 primary analysis. ORR (95% confidence interval [CI]) by ICR was 49.2% (35.9–62.5%) in Gp 1, 39.3% (26.5–53.2%) in Gp 3, and 44.3% (35.1–53.9%) for both gps combined. ORR by investigator assessment was 49.2% (35.9–62.5%) in Gp 1, 51.8% (38.0–65.3%) in Gp 3, and 50.4% (41.0–59.9%) combined. Median duration of response (DOR) per ICR has not been reached (range: Gp 1, 2.8–21.6 mos; Gp 3, 2.1–11.1 mos). Estimated 12-month DOR (95% CI) per ICR was 88.9% (69.3–96.3%) in Gp 1 and not evaluable in Gp 3. Similar proportions of pts in both gps experienced an adverse event (AE), most commonly diarrhea, fatigue, and nausea (Table). Grade ≥3 AEs were reported in 45.2% (52/115) of pts in both gps combined, most commonly anemia (6.1%, 7/115). Conclusions The primary analysis of Gp 3 confirms that the approved dose of cemiplimab 350 mg IV Q3W confers comparable efficacy and safety to the weight-based regimen (Gp 1) in mCSCC. Responses in both mCSCC cohorts were durable. Table:1318PGroup 1 (IV cemiplimab 3 mg/kg Q2W) n = 59Group 3 (IV cemiplimab 350 mg Q3W) n = 56Total n = 115DemographicsMedian age, years (range)71 (38–93)71 (38–90)71.0 (38–93)Male, n (%)54 (91.5)48 (85.7)102 (88.7)Eastern Cooperative Oncology Group performance status score = 0, n (%)23 (39.0)25 (44.6)48 (41.7)Eastern Cooperative Oncology Group performance status score= 1, n (%)36 (61.0)31 (55.4)67 (58.3)Primary CSCC site: Head and neck38 (64.4)31 (55.4)69 (60.0)Prior cancer-related systemic therapy33 (