The main goal of this first in human (FIH) study is to learn about the safety and dosing of GS-0201 when given alone or in combination with sacituzumab govitecan (SG) in participants with advanced solid tumors. The primary objectives of this study are to: * To assess the safety and tolerability of GS-0201 as monotherapy and in combination with SG in participants with selected advanced solid tumors * To identify the maximum tolerated dose (MTD) and/or the recommended Phase 2 dose (RP2D) of GS-0201 as monotherapy and the MTD and/or the RP2D and dosing schedule of GS-0201 in combination with SG in participants with selected advanced solid tumors