This prospective observational study investigates the clinical utility of circulating tumor DNA (ctDNA) in patients with oligometastatic disease (OMD) undergoing definitive-intent local ablative treatment (LAT). The study aims to evaluate ctDNA as a prognostic and response biomarker before, during, and after LAT across cancer types and treatment modalities. Serial plasma samples and archival tumor tissue will be analyzed to assess ctDNA detection rates, elimination patterns, minimal residual disease, and association with recurrence, progression, and survival outcomes.