Phase I Study of [225Ac]Ac-ETN029 in Patients With Advanced DLL3-expressing Solid Tumors

Inclusion Criteria: * Age ≥ 18 years old * Patients with one of the following indications: * Locally advanced, unresectable, or metastatic SCLC with disease progression following, or intolerance to, at least 1 line of systemic therapy, including platinum-containing chemotherapy, unless patient was ineligible to receive such therapy. Prior DLL3-targeted therapy is allowed. For dose expansion, patients should have received no more than 2 prior lines of systemic therapy. * Dose escalation only: LCNEC of the lung with disease progression following, or intolerance to, at least 1 line of systemic therapy, including platinum-containing chemotherapy, unless patient was ineligible to receive such therapy. * Dose expansion only: Locally advanced, unresectable, or metastatic de novo or castration-resistant, treatment-emergent NEPC with neuroendocrine differentiation confirmed by local histology and NEPC marker expression (e.g., chromogranin, synaptophysin) confirmed by local IHC. Prior PSMA-targeted, Lu-177-based RLT is allowed. Patients must have at least one measurable lesion (per RECIST 1.1) that shows 111In-ETN029 uptake higher than surrounding tissues on SPECT/CT as assessed by the Investigator. * Dose expansion only: Locally advanced, unresectable, or metastatic GEP-NEC with disease progression following, or intolerance to, at least 1 line of systemic therapy, including platinum-containing chemotherapy, unless patient was ineligible to receive such therapy. Patients must have at …