Evaluation of a 29 gene classifier for basal/non basal prediction in muscle-invasive bladder cancer FFPE samples.

467Background: Recent and independent muscle-invasive bladder cancer (MIBC) molecular classifications identified the basal / squamous-like (BASQ) tumours as an intrinsic and robust subtype, with a poor outcome and possible chemosensitivity to cisplatin based regimen, making mandatory the development of a diagnostic tool for their identification in routine samples. Our study aimed to evaluate the diagnostic accuracy of a Nanostring classifier for tumor subtype prediction on FPPE specimens. Methods: Two series of MIBC were used (CIT n = 51 & Stransky n = 22) for which BASQ tumours were identified previously using Affymetrix transcriptome data obtained from frozen samples (Rebouissou, Science Trans Med 2014). 29 genes were selected to predict the basal subtype, RNA expression of matched frozen and FFPE samples was studied using Nanostring technology. To define the classifiers for Affymetrix, frozen and FFPE Nanostring expression matrix on CIT samples the centroid of each cluster was calculated using the expr...