A Study to Evaluate the Safety and Efficacy of Gocatamig (MK-6070) and Ifinatamab Deruxtecan (I-DXd) in Participants With Relapsed/Refractory Extensive-Stage Small Cell Lung Cancer (MK-6070-002)

Researchers are looking for new ways to treat people with extensive-stage small cell lung cancer (SCLC) that has relapsed or is refractory. Gocatamig is a new type of immunotherapy that uses a person's immune system to find and destroy cancer cells. Ifinatamab deruxtecan (also known as I-DXd) is a drug which binds to a specific target on cancer cells and delivers treatment to destroy those cells. Durvalumab is a different type of immunotherapy that also destroys cancer cells. Researchers want to know if giving gocatamig, I-DXd, and gocatamig with I-DXd or durvalumab can treat SCLC that did not respond or stopped responding to a prior treatment. The goals of this study are to learn: * If gocatamig alone, I-DXd alone, and gocatamig with I-DXd or durvalumab are safe and well tolerated * If people who receive gocatamig alone, I-DXd alone, and gocatamig with I-DXd or durvalumab have their SCLC get smaller or go away

This study will consist of two parts. Part 1 will assess the safety, tolerability, and efficacy of gocatamig and I-DXd at doses determined in study MK-6070-001 (NCT: NCT04471727). Part 2 will assess the safety and tolerability of gocatamig in participants in Japan and China. Part 3 will assess the safety, tolerability, and efficacy of gocatamig with durvalumab.

Inclusion Criteria: * Has histologically or cytologically confirmed SCLC that is extensive stage (defined as Stage IV (T any, N any, M1a/b/c) following at least 1 prior line of systemic therapy that included platinum-based chemotherapy * Must be able to provide archival tumor tissue sample or fresh biopsy tissue sample * Human immunodeficiency virus (HIV) infected participants must have well controlled HIV on antiretroviral therapy (ART) Exclusion Criteria: * Pleural effusion, pericardial effusion, or ascites requiring recurrent drainage procedure * History of interstitial lung disease (ILD)/pneumonitis irrespective of steroid use or has current or suspected pneumonitis/ILD that cannot be ruled out by imaging at screening * Has clinically severe pulmonary compromise resulting from intercurrent pulmonary illnesses * Active or history of immune deficiency with the exception of HIV-infected participants with well controlled HIV on ART * History within 6 months before the first dose of study intervention of coronary/peripheral artery bypass graft and/or any coronary/peripheral angioplasty or clinically significant cardiovascular disease such as myocardial infarction, symptomatic congestive heart failure (CHF) (New York Heart Association \> class II), and/or uncontrolled cardiac arrhythmia * History of arterial thrombosis (eg, stroke or transient ischemic attack) within 6 months before the first dose of study intervention * Active clinically significant infection requiring systemic therapy * History of allogeneic tissue/solid organ transplant * History of leptomeningeal disease * Received prior radiotherapy within 2 weeks of start of study intervention, or has radiation-related toxicities, requiring corticosteroids * Receiving chronic systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of chronic immunosuppressive therapy within 7 days prior to the first dose of study intervention * Known additional malignancy that is progressing or has required active treatment within the past 3 years * Untreated or symptomatic brain metastases * Active viral hepatitis, defined as hepatitis A (hepatitis A virus immunoglobulin M \[IgM\] positive in the setting of associated signs/symptoms), hepatitis B (hepatitis B virus surface antigen \[HbsAg\] positive and/or detectable hepatitis B virus \[HBV\] deoxyribonucleic acid \[DNA\]), or hepatitis C (hepatitis C virus \[HCV\] antibody positive and detectable HCV ribonucleic acid). Participants with HBV with undetectable viral load after treatment are eligible. Participants with HCV with undetectable virus after treatment are eligible. * Part 1 only: Radiation therapy to the lung \>30 Gy within 6 months before the start of study intervention * Part 1 only: Abdominal radiation within 4 weeks before start of study intervention * Part 1 only: Anticancer hormonal treatment (except luteinizing hormone-releasing hormone \[LHRH\]) within 2 weeks before start of study intervention * Part 1 only: Systemic anticancer therapy (except antibody-based anticancer therapy) or investigational agents within 3 weeks or 5 half-lives, whichever is longer * Part 1 only: Antibody-based cancer therapy within 3 weeks before start of study intervention * Part 1 only: Chloroquine/hydroxychloroquine within 2 weeks before start of study intervention * Part 1 only: Clinically significant corneal disease * Part 1 only: Has other uncontrolled or significant protocol-specified cardiovascular disease