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)

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
* Any history of interstitial lung disease (ILD)/pneumonitis irrespective of steroid use except for a history of radiation pneumonitis that did not require steroids
* Current history of ILD or clinical or radiographic suspicion of ILD for which the diagnosis of ILD cannot be ruled out
* 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