Additional Study Information: The purpose of this study is to find out, as a main objective, at which doses RO6958688 (study drug) can be administered safely to subjects in combination with atezolizumab (study drug), and what the side effects are when both drugs are given together. Additionally, the effects of RO6958688 and atezolizumab in the body, and particularly in the tumor, will be evaluated. The study also aims to find out if RO6958688 in combination with atezolizumab can slow down the growth of tumors or stop the cancer, in subjects with locally advanced and/or metastatic solid tumors. This study is for subjects whose tumors cells express the carcinoembryonic antigen (CEA), which is the target of RO6958688.