This is a two-arm, randomized, double blind, placebo-controlled study of Optune (Tumor Treating Fields at 200 kHz) to the brain concomitant with maintenance Temozolomide (TMZ) chemotherapy agent and pembrolizumab compared to Optune concomitant with maintenance TMZ and placebo in newly diagnosed Glioblastoma (GBM) patients. The primary objective of the study is to evaluate the Overall Survival (OS).