This is a prospective, single-centre feasibility study of CSF ctDNA conducted at the Sunnybrook Odette Cancer Centre (SOCC), Toronto, Canada, including multiple solid tumor, stratified into cohorts according to CNS disease involvement, including leptomeningeal disease (Cohort A), parenchymal brain metastases (Cohort B), and no evidence of CNS metastases (Cohort C).
Patients in Cohort A will have previously untreated or progressing leptomeningeal metastatic disease (LMD) with or without parenchymal brain metastases (BrM).
Patients in Cohort B will have previously untreated or BrM but no evidence of LMD.
Patients in Cohort C will have progressing extra-cranial metastatic disease with no LMD or BrM.
Patient is suitable for lumbar puncture and/or has an Ommaya reservoir that is accessible for CSF collection.
Inability to understand or unwillingness to provide written informed consent (language barriers are not exclusionary; the use of a translator is permitted).
Patients with contraindications to lumbar puncture (e.g., infection at the LP site, uncontrolled bleeding diathesis > 1.5], severe thrombocytopenia [platelet count <40,000/µL], use of anticoagulant or antiplatelet medications cannot be safely interrupted, significant mass effect with risk of herniation, or presence of vertebral hardware)