ANGI-06. CEREBROSPINAL FLUID MAY BE THE MOST IMPORTANT PATHWAY FOR BRAIN METASTASES: A DATA-DRIVEN HYPOTHESIS AND CLINICAL IMPLICATIONS

Abstract INTRODUCTION Hematogenous spread of brain metastases represents conventional wisdom. However, compelling physiologic evidence suggests that brain metastases may reach the CNS by way of the CSF either via the choroid plexus or directly from the bone marrow. We provide clinical evidence that invasion of brain parenchyma occurs through the CSF, and we model the therapeutic implications of this novel hypothesis. METHODS First, we assessed whether brain metastases were contiguous with a CSF space in 204 consecutive patients using pre-treatment MRI. Then, CSF was examined for malignant cells in 66 consecutive brain metastasis patients. Next, we contoured normal brain MRIs of 3 patients to calculate the percentage of brain within 5 mm of a CSF space. Finally, we queried an international neoplastic meningitis registry for patients with brain metastases to evaluate response to intra-CSF chemotherapy alone. RESULTS In 204 consecutive patients with brain metastases, the mean number of metastases was 4.63 (SD 6.26), and 85% of metastases touched a CSF space. In 67% of patients, all metastases touched a CSF space. In our consecutive cohort of 66 patients with CSF analysis, 44% with one, 46% with two, 63% with three, and 71% with >3 metastases had malignant cells in the CSF (R2=0.93, p=0.04). Brain contouring revealed that up to 75% of the brain parenchyma lies within 5 mm of a CSF space. Seven of 10 patients with both brain and CSF metastases receiving only intrathecal chemotherapy experienced disappearance or substantial reduction in the size of their metastases. CONCLUSIONS This data suggest that brain metastases may access the CNS through the CSF. Intrathecal chemotherapy can reach most brain metastases and can produce objective responses. We suggest that the CSF should be monitored in all patients with, or at risk for, brain metastases, and true cures may require treatment of the CSF space.