Patients with small cell lung cancer (SCLC) have poor prognosis and limited treatment options beyond first-line therapy. Secondary endpoints include ORR by investigator; progression-free survival, duration of response, disease control rate, and time to response, all by BICR and investigator; patient-reported outcomes; and safety. IDeate-Lung02 will ascertain whether I-DXd treatment after only one prior line of systemic treatment improves outcomes for patients with relapsed SCLC compared with topotecan, amrubicin, or lurbinectedin.Clinical Trial Registration: NCT06203210.