BackgroundCutaneous squamous cell carcinoma (CSCC) is the second most common skin cancer in white-skinned populations. Advanced or metastatic disease is rare, less than 5% of patients (pts), but when it occurs, is difficult to treat and often has a poor prognosis. Immune checkpoint blockade with cemiplimab, a PD-1 inhibitor, has been approved for advanced/metastatic CSCC1 were is getting excellent results.2 However, unlike what is already standard pratice for melanoma skin cancer,3 4 we do not know yet which is the optimal treatment duration. The aim of this study is to evaluate the minimum treatment period with cemiplimab in order to guarantee a durable clinical benefit.MethodsIn this retrospective study was evaluated the duration standard treatment with cemiplimab 350 mg every 3 weeks (Q3W) in 95 pts with CSCC, on which 22 were discontinued not by clinical decision (figure 1). Demographic and clinical data were tabulated using descriptive statistics. PFS was calculated as the time from randomization until objective tumor progression or death, whichever occurs first; OS was calculated from randomization until death by any cause.ResultsOverall, 95 pts were enrolled. Demographic and clinical characteristics are reported in table 1. The median age was 75 years (range, 32–96 years), and 68 (72%) pts were males. Cemiplimab was administered as first-line therapy in 45 (47%) pts and as second-line in 50 (53%) subjects; The most frequent comorbidities were blood hypertension (51%) and angina/coronary artery disease (23%). At the first follow-up visit, 10 (11%) pts achieved CR, 25 (26%) PR, 35 (37%) reached SD, and 25 (35%) were in progression. Twenty-two stopped cemiplimab treatment due to comorbidity (n=7), toxicity (n=3), no compliant (n=9) and complete response (n=3). No significant difference was observed in this cohort compared to general population (figure 2) in terms of OS (p=0.47; HR 0.80 (95% CI 0.42 to 1.48)) and PFS (p=0.29; HR 0.72 (95% CI 0.39 to 0.32). In the swimmer plot cartoon (figure 3), we observed 10 death events in pts treated for less than a year (n=12), only 1 death in pts treated at least 1 year (n=10) and 0 death in pts treated at least 2 years (n=5) (figure 4).ConclusionsFrom a patients, healthcare, and economic perspective, shorter treatment duration is preferred, and overtreatment should be prevented. In these preliminary result we showed that at least one year of treatment with cemiplimab appears to be a valid option. Further investigations are needed to get additional information.ReferencesGoodman DT. Cemiplimab and Cutaneous Squamous Cell Carcinoma: From Bench to Bedside. JPRAS Open. 2022 Jun 23;33:155−160. doi: 10.1016/j.jpra.2022.06.003.Baggi A, Quaglino P, Rubatto M, Depenni R, Guida M, et al. Real world data of cemiplimab in locally advanced and metastatic cutaneous squamous cell carcinoma. Eur J Cancer. 2021 Nov;157:250−258. doi: 10.1016/j.ejca.2021.08.018.Mulder EEAP, de Joode K, Litière S, Ten Tije AJ, Suijkerbuijk KPM, et al. Early discontinuation of PD-1 blockade upon achieving a complete or partial response in patients with advanced melanoma: the multicentre prospective Safe Stop trial. BMC Cancer. 2021 Mar 25;21(1):323. doi: 10.1186/s12885-021-08018-w.Coen O, Corrie P, Marshall H, Plummer R, Ottensmeier C,et al. The DANTE trial protocol: a randomised phase III trial to evaluate the Duration of ANti-PD-1 monoclonal antibody Treatment in patients with metastatic mElanoma. BMC Cancer. 2021 Jul 1;21(1):761. doi: 10.1186/s12885-021-08509-w.Ethics ApprovalThis study was approved by the Ethics Committee of National Cancer Institute—IRCCS—Fondazione ‘‘G. Pascale’’, Naples, Italy, protocol number 32/22 oss. All patients provided their written informed consent to participate in this study.ConsentWritten informed consent was obtained from the patient for publication of this abstract and any accompanying images. A copy of the written consent is available for review by the Editor of this journalAbstract 579 Figure 1Abstract 579 Figure 2Abstract 579 Figure 3Abstract 579 Figure 4Abstract 579 Table 1