The investigators are interested in one of the most frequent tumor types causing leptomeningeal metastasis in order to investigate whether a profile can be established by a high-throughput clinical proteomic approach. All the data acquired will allow a tailored and promising approach to improve the knowledge of metastatic tumor meningitis.

The primary objective is to describe on an exploratory basis the association between the type of proteomic profile from cerebrospinal fluid (CSF) microvesicles (from unsupervised bioinformatics analysis) and CSF cytology analysis (positive, negative, equivocal) in breast cancer patients with suspected leptomeningeal metastases, on initial CSF samples (hereafter referred to as initial proteomic profile and initial cytology).

Inclusion Criteria:

• Patient with histologically proven breast cancer;
• Patient with suspected metastatic leptomeningeal involvement;
• Age ≥ 18 ans ;
• WHO performance status ≤ 2 ;
• Affiliation to the National Social Security System ;
• With informed and signed consent

Exclusion Criteria:

• History of another cancer than the one for which the patient is referred;
• Contraindication to lumbar puncture or cerebrospinal MRI
• Pregnant or breastfeeding woman

Breast cancer