VET3-TGI is an oncolytic immunotherapy designed to treat advanced cancers. VET3-TGI has not been given to human patients yet, and the current study is designed to find a safe and effective dose of VET3-TGI when administered by direct injection into tumor(s) (called an intratumoral injection) or when given intravenously (into the vein) both alone and in combination with pembrolizumab in patients with solid tumors (STEALTH-001).