A Phase I Study to Evaluate the Safety and Preliminary Efficacy of [225Ac]Ac-DOTATATE Injection Combined With Tislelizumab in the Maintenance Treatment Period for Patients of Extensive-stage Small Cell Lung Cancer (ES-SCLC) With Somatostatin Receptors (SSTR)+ as First-line Treatment

This study tests whether a targeted radioactive treatment called [225Ac]Ac-DOTATATE, combined with the immunotherapy drug tislelizumab, is safe and shows early signs of effectiveness as a maintenance therapy for people with extensive-stage small cell lung cancer (ES-SCLC) whose tumors express a certain receptor (SSTR) and who responded to initial first-line therapy. **You may be eligible if...** - You are 18 to 80 years old - You have confirmed extensive-stage small cell lung cancer - Your tumor scans are positive for somatostatin receptors (SSTR-PET positive) - Your cancer has at least one measurable site of disease - Your performance status is good (ECOG 0 or 1) - Your blood counts and organ function are within acceptable limits **You may NOT be eligible if...** - You are pregnant or breastfeeding - You have received prior systemic anti-cancer treatment within 4 weeks before starting study treatment - You have uncontrolled heart failure or uncontrolled diabetes - You have a known allergy to the study drugs - Your doctor believes another treatment option is more appropriate for you Talk to your doctor to see if this trial is right for you.