Clinical Utility of ctDNA in the Treatment of Oligometastatic Disease

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.

Oligometastatic disease (OMD) represents an intermediate disease state between localized and polymetastatic cancer and may be amenable to curative or long-term disease-controlling local ablative treatment (LAT). Despite careful patient selection, recurrence rates after LAT remain substantial, highlighting the need for improved biological markers to guide treatment decisions and follow-up. Circulating tumor DNA (ctDNA) is a promising biomarker for prognostication, response assessment, and early detection of recurrence. Pilot studies and systematic reviews conducted by the study group indicate that ctDNA dynamics before and after LAT are associated with treatment outcomes. However, important knowledge gaps remain regarding ctDNA detection rates, elimination patterns, optimal sampling time points, and clinical relevance across metastatic sites, treatment modalities, and oligometastatic states. This prospective observational study, conducted as part of the Pan-Cancer Oligometastatic Biology (POB) project, will enroll patients with oligometastatic solid tumors planned for definitive-intent LAT. Serial blood samples will be collected before treatment, during treatment when applicable, and throughout follow-up. ctDNA and total circulating free DNA will be analyzed using sensitive molecular techniques. Archival tumor tissue will be retrieved for tumor-informed analyses. The study will evaluate ctDNA detection rates, elimination patterns, minimal residual disease, lead time to radiological recurrence, and associations with disease-free survival, progression-free survival, and overall survival. Exploratory analyses of immune-related biomarkers will also be performed. The results are expected to support improved biological stratification and monitoring strategies in oligometastatic disease.