A Study of I-DXd in Combination With Atezolizumab With or Without Carboplatin as First-Line Induction or Maintenance in Subjects With Extensive Stage-Small Cell Lung Cancer (IDeate-Lung03)

A full list of inclusion/

are available in the protocol. Inclusion Criteria Participants must meet all of the following criteria to be eligible for enrollment into the study: 1. Sign and date the informed consent form (ICF), prior to the start of any study-specific qualification procedures. 2. Adults ≥18 years or the minimum legal adult age (whichever is greater) at the time the ICF is signed. 3. Has histologically or cytologically confirmed diagnosis of ES-SCLC who will require first-line (IL) therapy. 4. For Cohort 1, participant has received 4 cycles of 1L induction therapy with carboplatin, etoposide, and atezolizumab for ES-SCLC with ongoing CR PR, CR, or SD per RECIST v1.1 assessed by the investigator. For Cohort 2, participant has received no prior treatment for ES-SCLC. 5. For Cohort 2, participant has at least one measurable lesion according to RECIST v1.1 on computed tomography (CT) or magnetic resonance imaging (MRI) as assessed by the investigator. 6. For Cohort 2, participant must have at least one lesion, amenable to core biopsy, and must consent to provide a pretreatment biopsy tissue sample and on-treatment biopsy. 7. Has ECOG PS of ≤1 (assessed within 7 days before enrollment/randomization). 8. Has adequate organ and bone marrow function within 7 days before the start of study treatment as specified in the study protocol. 9. A female subject of childbearing potential (POCBP) is eligible to participate if the following conditions are met: 1. Subject is not pregnant as confirmed by highly sensitive pregnancy test during Screening (within 3 days prior to enrollment/randomization) 2. Subject does not breastfeed during the treatment period and for at least 8/5/6 months after last dose of I-DXd/atezolizumab/carboplatin, respectively. 3. Subject agrees to adhere to a contraceptive method that is highly effective and agrees not to donate eggs (ova, oocytes) to others or freeze/store eggs during the treatment period and for at least the time needed to eliminate each study drug after the last dose. The length of time required to continue contraception and avoid donating/freezing eggs after last dose for I-DXd/atezolizumab/carboplatin is 8/5/6 months, respectively. Preservation of eggs may be considered prior to first dose of study drug. 10. A male subject capable of producing sperm is eligible to participate if he agrees to the following during the intervention period and for at least the time needed to eliminate each study drug. The length of time required to continue contraception and avoid donating sperm after last dose for I-DXd/atezolizumab/carboplatin is 6/5/6 months, respectively. 1. Avoid donating sperm. 2. Adhere to either of the contraception methods: true abstinence from penile-vaginal intercourse or uses a penile/external condom when having penile-vaginal intercourse with a non-subject of childbearing potential plus partner use of an additional contraceptive method. 11. Is willing and able to comply with scheduled visits, drug administration plan, laboratory tests, other study procedures, and study restrictions.