“…In another study by Berghoff et al [16] a single-center retrospective analysis ("Vienna cohort"), improved survival was not associated with TIL density (or PD-L1 overexpression), in contrast the other studies. Routine analysis of TILs is difficult in clinical settings, so it is crucial that the study of Alexiou et al [6,7] mirrors the use of serum kynurenine and tryptophan levels as another biomarker of the immunosuppressive effect of IDO catabolism in gliomas, which demonstrated prognostic significance for OS in a prospective, multi-center observational trial of GBM patients. [17] Taken together, the work of Alexiou et al, [6] Bambury et al, [9] and Han et al [15] elaborate upon the role of TILs in GBM via an easily obtainable, non-invasive, serum biomarker proxy.…”