PIK3CB and glioblastoma: To gain an overview of the expression pattern of class IA PI3K isoforms and the activation of the PI3K/Akt/mTOR signaling pathway in GBM cell lines and ex vivo cultures, we performed Western blot analysis on a set of seven GBM cell lines and seven ex vivo (EV) cultures (Figure 1C and Tables S3 and S4).