CO80 Surrogate Endpoints for Overall Survival in Cutaneous Squamous Cell Carcinoma: A Meta-Regression of Clinical Trials

Objectives:
Cutaneous squamous cell carcinoma (CSCC) is the second most common skin cancer. Treatment of advanced CSCC has traditionally been performed with chemotherapies with predominately poor results. Recently Immunotherapy (IO) has shown promising effectiveness, however the overall survival reported from these trials is immature (i.e. median is yet to be reached). This poses challenges for payers and decision makers as economic modelling and evaluation are heavily dependent on overall survival (OS). The objective of this study is to identify surrogate endpoints for OS that can be used to establish whether next generation therapies are cost-effective for CSCC.

Methods:
Clinical trials for the treatment of CSCC were obtained from the literature. Data extracted from each trial were: proportion of patients with metastatic disease, progression free survival (PFS), OS, type of treatment (chemotherapy, tyrosine kinase inhibitor (TKI) or IO), objective response rate (ORR). A meta-regression was performed using R on a Windows 10 platform.

Results:
Six clinical trials investigating treatments for CSCC were identified. All were single arm trials, with three chemotherapy trials, two TKI trials and one IO trial. PFS was the only factor from the meta-regression that was significant (p=0.0422). The other factors: metastatic disease (p=0.1724), treatment (p=0.2100) and ORR (p=0.4658) were non-significant. No heterogeneity was observed (I-square=0%). The meta-regression estimated the PFS contribution to be 2.99 [95% CI: 2.38 to 3.61]. This means that an observed PFS of 18.4 months was estimated to lead to an OS of 55.0 months [95% CI: 43.6 months to 66.3 months].

Conclusions:
Only PFS is observed to be significantly associated with OS based on the current trial evidence. This study demonstrates that PFS can be regarded as a surrogate for overall survival in CSCC.