The main goal of this first in human (FIH) study is to learn about the safety and dosing of GS-9911 when given alone or in combination with an anti-programmed cell death protein 1 (PD-1) monoclonal antibody in participants with advanced solid tumors. The primary objectives of this study are to: * Assess the safety and tolerability of GS-9911 as monotherapy and in combination with an anti-PD-1 monoclonal antibody in participants with advanced solid tumors * Identify the maximum tolerated dose (MTD)/maximum administered dose (MAD) and the recommended dose for expansion (RDE) of GS-9911 as monotherapy and in combination with an anti-PD-1 monoclonal antibody in participants with advanced solid tumors