The purpose of this study is:

Phase I: To determine the Trastuzumab maximum tolerated dose (MTD) when weekly administrated by intrathecal or intraventricular route to reach a intra CSF target concentration (30 µg/mL) near the conventional therapeutic concentration and depending on the dose-limiting toxicity (DLT)

Phase II: Determination of antitumor activity trastuzumab when administrated by IT or intra-ventricular in terms of neurological progression-free survival at 2 months

Phase I: Secondary Outcome Measures:

Recommended dose (RD will be used in Phase II) Toxicity during treatment Clinical response to specific neurologic symptoms Time to neurologic progression Biological response: CSF cellularity and protein concentration Radiological response: cerebrospinal meningitis and neuraxis RMI Impact on quality of life Impact on survival (overall survival, survival without neurological progression, progression-free survival) Pharmacokinetics: dose of trastuzumab in CSF and plasma FCGR3A Genetic status influence on efficacy trastuzumab in metastatic breast cancer

Phase II: Secondary Outcome Measures :

Toxicity during treatment Clinical response to specific neurologic symptoms Time to neurologic progression Biological response: CSF cellularity and protein concentration Radiological response: cerebrospinal meningitis and neuraxis MRI Impact on quality of life Impact on survival (overall survival, survival without neurological progression, progression-free survival) Pharmacokinetics: dose of trastuzumab in CSF and plasma (confirmation of phase I data with 5 patients) FCGR3A Genetic status influence on efficacy trastuzumab in metastatic breast cancer

Inclusion Criteria:

• Metaplastic Infiltrating adenocarcinoma of the breast
• HER2 Overexpression by IHC and / or amplification (FISH and or ICHS)
• Positive diagnosis of neoplastic meningitis: positive CSF cytology (obtained within 28 days before inclusion) AND / OR clinical symptoms of neoplastic meningitis and aspect of tumoral meningitis on MRI
• Brain metastases are allowed without prior treatment, if they are asymptomatics and without engagement. In cases of symptomatic brain metastases, subjects could be included only if surgery and / or radiotherapy (stereotactic or in toto) were performed and if the cerebral metastatic localization allow IT or intra-ventricular treatment. The last radiotherapy session or the surgery must have been done 3 weeks before.
• Aged 18 years old or more
• Male and female
• Life expectancy more than 2 months
• Satisfactory Cardiac function: left ventricular ejection fraction (LVEF) determined by ultrasound scan or myocardial scintigraphy
• Adequate Biological functions 14 days before inclusion, according to the criteria below: Neutrophils > 1.0 x 109/L, Hemoglobin > 9.0 g/dL (+ transfusion if needed,Platelets > 50 x 109/L,Bilirubin < 3 x N, ALT & AST < 10 x N, Creatinine < 2.0 mg/dL, Clearance > 25 mL/min (Cockcroft and Gault formula), Prothrombin time > 70 %, Kaolin cephalin coagulation time < 1.5 x N.
• Women of childbearing potential, must take adequate birth control measure during the study period and must have a negative pregnancy test (BetaHCG serum)
• The subjects must perform all evaluations of pre-inclusion, as provided by the protocol
• Signed written inform consent

Exclusion Criteria:

• CSF circulation disorders suspected on MRI brain (obstructive hydrocephalus) or medullar (obstacle) with, in case of a focal radiotherapy on obstructive lesion, checking the restoration of transit traffic by isotope CSF
• Anti-coagulant effective dose treatment when trastuzumab administration by lumbar puncture
• Patient on Lapatinib (wash out> 2 weeks from the date of first dose intrathecal trastuzumab)
• Known or suspected trastuzumab allergy
• Contraindications of trastuzumab administration, including cardiac diseases: LVEF \