BSLD-10 CHARACTERIZATION OF CEREBROSPINAL FLUID TO BETTER ANTICIPATE SYSTEMIC PROGRESSION OF CANCERS IN PATIENTS WITH LEPTOMENINGEAL CARCINOMATOSIS (LMC): DUAL INSTITUTIONAL ANALYSIS

Abstract PURPOSE Leptomeningeal carcinomatosis (LMC) is a rapidly fatal metastasis of systemic cancer to the leptomeninges commonly treated with intrathecal (IT) chemotherapy. Earlier identification of progression or treatment effects could earlier inform failing response to systemic therapy and extend patient quality survival. QUESTION Are there measurable changes in cerebrospinal fluid (CSF) associated with systemic cancer progression in LMC patients treated with IT chemotherapy? METHODS We retrospectively analyzed CSF and imaging data for LMC patients treated with IT chemotherapy between 2017–2025 as part of established Ommaya Clinics. We identified dates of systemic progression as determined by body CT/PET scans over the patient’s treatment course. We then evaluated CSF changes in protein, glucose, and white blood cells (WBCs) 6–8 weeks prior to noted systemic progression. RESULTS Of 123 patients evaluated, 51% (n=63) developed 1st or 2nd radiographically assessed systemic disease progressions while being treated with IT chemotherapy. Of these progressed cases, 70% (n=44) were preceded within 6 weeks by an average protein elevation of 32 mg/dL, 79% (n=50) showed an average WBC elevation of 2 cells/mm3, and 35% (n=22) had an average glucose reduction of 14 mg/dL as compared to serum glucose. Seventy-two percent of patients did not have clear worsening neurologic deficits obvious clinical decline prior to radiographic progression. CONCLUSIONS There are measurable changes in CSF markers that precede systemic and CNS events in cancer patients undergoing IT therapy. Accurate assessment of these markers has potential implications for predicting systemic progression and offers a window of opportunity for earlier therapeutic intervention, limiting clinical decline, and informing treatment response.