A Study of GSK5764227 in Participants With Relapsed Small Cell Lung Cancer (SCLC) [EMBOLD SCLC-301]

Inclusion Criteria:

Participants are eligible to be included in the study only if all of the following criteria apply:

* Adults \>18 or the minimum legal adult age at the time the informed consent form is signed
* Has histologically or cytologically confirmed extensive-stage small cell lung cancer (ES-SCLC).
* Has received 1 prior platinum-based systemic therapy with a PD- (L)1 inhibitor for at least 2 cycles of therapy and a chemotherapy free-interval of \>30 days, with documented progression. Participants with prior tarlatamab treatment in either the first- or second-line ES-SCLC setting are eligible.
* Has at least 1 target lesion per RECIST 1.1, as determined by the investigator.
* Is capable of giving signed informed consent, including compliance with the requirements and restrictions listed in the ICF and in the protocol.
* Has adequate organ function and an ECOG performance status of 0 or 1

Exclusion Criteria:

Participants are excluded from the study if any of the following criteria apply:

* Pathological diagnosis of complex SCLC or transformed SCLC.
* Limited stage small cell lung cancer at diagnosis
* Has received any prior therapy with an Antibody-drug conjugate (ADC) with a Topoisomerase-1 (TOPO1)-inhibitor payload or treatments targeting B7-H3.
* Has known sensitivity to study intervention components or excipients or other allergy that, in the opinion of the investigator or medical monitor, contraindicates participation in the study.
* Has severe, uncontrolled or active cardiovascular disorders.
* Has clinically significant bleeding symptoms or significant bleeding tendency within 1 month prior to the first dose.
* Known active infectious diseases requiring systemic treatment or known Human immunodeficiency virus (HIV).
* Has symptomatic brain metastases or untreated progression exclusively due to brain metastasis during or after the last treatment prior to screening, evidence of leptomeningeal/meningeal/brainstem metastasis or evidence of spinal cord metastases.
* Has any evidence of current interstitial lung disease or pneumonitis or a prior history of ILD or non-infectious pneumonitis requiring high dose steroids.
* Has significant pulmonary disease or respiratory impairment (e.g., uncontrolled asthma/COPD, restrictive lung disease),
* Has active Hepatitis B or Hepatitis C