Analysis of cell-free tumor DNA in cerebrospinal fluid as a diagnostic biomarker for leptomeningeal melanoma metastasis: a case series

Introduction: leptomeningeal metastases (LMM) in melanoma are associated with poor survival. Diagnosis is based on MRI findings and detection of melanoma cells with cytological examination of the cerebrospinal fluid (CSF). Ambiguous results often delay treatment initiation in this urgent medical setting. We report a single center case series in which detection of BRAFV600E/D- and NRASQ61R/K-mutations on cell-free tumor DNA (ctDNA) in CSF was used as a complementary diagnostic biomarker. Materials & Methods: retrospective review of medical records of melanoma patients with clinical suspicion of LMM, in whom MRI of the brain, cytological/biochemical CSF analysis were performed and complemented with ctDNA analysis on 1 ml of CSF, using the fully automated Idylla® platform. Results: 9 patients were included (7 female, median age 55.7y; 6 BRAFV600-, 2 NRASQ61-mutant, one mutational status was unknown prior to CSF analysis). At the time of first CSF analysis, patients had stage IV-M1c (n=4) and IV-M1d (n=5) melanoma. In all patients LMM were suspected clinically. The most frequent symptoms were headache (n=6), a focal neurological deficit (n=6), vertigo (n=4) and nausea (n=3). 6 patients had MRI abnormalities, indicative of LMM. CSF analysis revealed malignant cells in 2 patients (1 with MRI abnormalities). BRAFV600E/D- or NRASQ61R/K-mutant ctDNA was detected in the CSF analysis of 5 patients (4 of 6 with-, and 1 of 3 patients without MRI abnormalities and in both patients with positive CSF cytology). Progressive LMM were confirmed in all patients with positive CSF ctDNA analysis during follow-up. In one additional patient, a second CSF analysis revealed the known BRAFV600E -mutation and the emergence of an acquired NRASQ61-mutation during BRAF-/MEK-inhibitor treatment. During follow-up, in patients with a negative CSF ctDNA analysis, 1 displayed LMM, the other 2 were proven not to be affected by LMM. Conclusion: analysis for BRAFV600- and NRASQ61-mutant ctDNA on CSF using the Idylla® platform holds promise as a sensitive and specific complementary biomarker for the diagnosis of LMM, especially in cases with ambiguous imaging or CSF cytology results. The rapid (90 min) analysis of 1 ml of CSF, offering same day results, can be of important benefit, facilitating urgent treatment