BIOM-05. CASE SERIES OF MULTI-INSTITUTIONAL UTILITY OF CNSide TO MANAGE LEPTOMENINGEAL DISEASE IN PATIENTS WITH METASTATIC BREAST CANCER

Abstract INTRODUCTION Leptomeningeal Disease (LMD) occurs in 5% of breast cancer patients. Diagnosing LMD remains challenging. Current standard of care has limited sensitivity and is inadequate for monitoring treatment response. Biocept’s CNSide™ is a proprietary assay utilizing a 10-antibody capture cocktail with microfluidic chamber that quantitatively detects tumor cells in the cerebrospinal fluid (CSF). We present a case series using CNSide to manage LMD of 4 unique breast cancer patients treated at three different institutions and demonstrate its impact on clinical management. METHODS Patients were treated at Smilow Cancer Hospital at Yale-New Haven (1 patient), Northwestern Medicine Lou and Jean Malnati Brain Tumor Institute (1 patient) and Barrow Neurological Institute (2 patients). All patients received intrathecal treatment (IT) via an Ommaya Reservoir. CSF tumor cells were detected via cytology and CNSide at diagnosis (3 patients) and throughout treatment (4 patients). RESULTS At diagnosis, CNSide detected tumor cells in 3/3 patients, vs 2/3 patients for cytology. The fourth patient was diagnosed with LMD before CNSide was available. CNSide detected CSF tumor cells in 9/9 (100%) of measurements, vs 4/9 (44%) for cytology for samples analyzed in parallel. Throughout treatment, CNSide was able to track the quantitative LMD response and showed a decrease in CSF tumor cells in all four patients, ranging from 99.7% (from 773 to 2 cells, 1 patient) to 100% (from 4447 to 0 cells; and from 33 to 0 cells, 2 patients). CONCLUSION Intrathecal treatment of LMD via Ommaya reservoir is not widely adopted across the US. Our experience suggests that using CNSide for quantitative CSF tumor cell detection may aid in diagnosing LMD, as well as in quantifying response to treatment particularly in the setting of intrathecal therapy. However, larger prospective clinical trials are needed to establish the role of CNSide in the diagnosis and management of LMD.