Study terminated due to strategic business decisions.

This study aims to determine safety, tolerability, recommended phase 2 dose (RP2D), and preliminary antitumor activity of 225Ac-SSO110 with standard of care (SoC) therapy in patients with somatostatin receptor 2 expressing (SSTR2+) extensive-stage small cell lung cancer (ES-SCLC) and recurrent locally advanced or metastatic Merkel cell carcinoma (MCC).

Key Inclusion Criteria:

• Signed Informed Consent Form and willing to comply with all study procedures.
• Participants with ES-SCLC (defined as Stage IV per NCCN guidelines Version 1.2024) or recurrent locally advanced or metastatic MCC (per NCCN guidelines Version 1.2024) documented by histology or cytology.
• Participants eligible to receive immune checkpoint inhibitor (CPI) monotherapy at the start of treatment with 225Ac-SSO110 or patients already on CPI monotherapy for 7 weeks.
• ECOG performance status of 0 or 1. Life expectancy of at least 6 months.
• Positive 68Ga-SSO120 scan (Investigator-assessed) during screening.

Key Exclusion Criteria:

• Participants with unstable spinal cord compression.
• Any previous systemic radioligand therapy or extensive radiotherapy.
• Participants receiving or planned to receive consolidative chest radiation.
• History of primary immunodeficiency, transplantation or CAR-T cell therapy.
• Major surgical procedure except diagnostic biopsy within 28 days prior to enrolment or scheduled to have major surgery during the study.
• Inadequate organ or marrow function.