Extensive molecular profiling of squamous cell anal carcinoma in a phase 2 trial population: Translational analyses of the "CARACAS" study

•In advanced squamous cell anal carcinoma no standard therapies in lines after the first are established.•CARACAS was the first randomised trial in advanced squamous cell anal carcinoma in advanced lines.•High PD-L1 conferred longer PFS; high tumour mutational burden was related to better overall survival .•This study documented prognostic value of tumour mutational burden and PD-L1 in advanced squamous cell anal carcinoma treated with immune checkpoint inhibitors .