The goal of this clinical study is to learn more about the study drug sacituzumab govitecan (SG; Trodelvy®; GS-0132; IMMU 132), versus standard of care (SOC) in participants with previously treated extensive stage small cell lung cancer (ES-SCLC). The primary objectives of this study are to compare the effect of SG to SOC on objective response rate (ORR) as assessed by blinded independent central review (BICR) according to the Response Evaluation Criteria in Solid Tumors and to compare the effect of SG to SOC on overall survival (OS).