159P - Prognostic immunoprofiling of muscle invasive bladder cancer (MIBC) patients in a multicentre setting

Introduction of checkpoint inhibitors (anti PD-1/PD-L1) have resulted in improved survival for bladder cancer patients, however, only a subset will benefit. The utility of PD-L1 expression as a prognostic or predictive biomarker is limited, motivating the search for more robust biomarkers. Here, we examined the prognostic value of densities of PD-L1, CD3, CD8 or CD68 positive cells and studied the reproducibility of the findings across two patient cohorts in a multi-assay and multicentre setting. MIBC specimens (T stage 2/3) from two patient cohorts collected at Melbourne, Australia (n=39) and University of St Andrews, UK (n=63) were studied. Two consecutive slides were stained with a brightfield immunohistochemistry or an immunofluorescence assay in the first and second cohorts, respectively. The densities of positive cells within the tumour core were determined using assay-specific image analysis algorithms. Within each cohort, the prognostic value of each cell density was assessed using univariate and multivariate Cox regression including age, T stage, N stage and adjuvant chemotherapy as covariates. The Melbourne cohort is slightly older, with a poorer prognosis and a higher proportion of N2/N3 disease compared to the St Andrews cohort. Univariate and multivariate analyses identified the density of CD8 positive cells as an important prognostic factor across both cohorts (p