Treatment of microstellite stable metastatic colorectal cancer presenting high immune infiltrate with chemotherapy (Xelox Bevacizumab) and immunotherapy ( Pembrolizumab)

Primary objectives: To evaluate the efficacy of pembrolizumab in combination with XELOX and bevacizumab as 1st line treatment of microsatellite stable (MSS) metastatic colorectal cancer (mCRC) with a high immune infiltrate. Efficacy will be determined by analysis of the number of patients alive and without radiological and/or clinical progression at 10 months (based on RECIST 1.1 criteria evaluated by the investigator). Primary endpoints: The primary endpoint is the percentage of patients alive and without progression at 10 months. Progression is defined by: - radiological progression evaluated by the investigator according to RECIST v1.1 criteria. - death, whatever the cause