PDCD1 and glioblastoma: ,47 Since arginase has been identified as a potential biomarker of disease progression, investigating the therapeutic efficacy of arginase inhibitors as monotherapy or in combination with PD-1/PD-L1 inhibitors has been of great research interest38,40,48, 49, 50, 51, 52 and a number of clinical trials are ongoing (Supplementary Table S2, available at https://doi.org/10.1016/j.esmoop.2022.100636) in advanced solid tumours and glioblastoma.