Safety and Efficacy of BNT327, an Investigational Therapy in Combination With Chemotherapy for Patients With Untreated Small-cell Lung Cancer

There are two stages in this study: Stage 1 will have two treatment arms and one control arm, and Stage 2 will have a treatment arm and a control arm. The control arms in Stages 1 and 2 are the same. Each stage of the study consists of a screening period (up to 21 days), an induction period followed by a maintenance period (until confirmed disease progression, intolerable toxicity, participant withdrawal, study termination or up to 2 years \[whichever occurs first\]), and a follow-up (FU) period for all participants (2 safety FU visits and survival FU visits). In Stage 1, eligible participants will be randomized (1:1:1) to the arms. In Stage 2, participants will then be randomized (1:1) to the arms. The randomization will be stratified based on the following factors: 1. Brain or liver metastases per investigator assessment (presence versus absence); 2. Smoking status (smoker versus never-smoker); and 3. Geography. Participants will be allowed to switch to cisplatin if carboplatin is not tolerated at the investigator's discretion.