The purpose of this study is to assess the safety and efficacy of masitinib for the treatment of mild to moderate Alzheimer's Disease. Masitinib will be administered as add-on therapy in patients who have been treated for a minimum of 6 months with a stable dose of cholinesterase inhibitor (donepezil, rivastigmine or galantamine) and/or memantine.

Actual standard treatment for mild to moderately severe Alzheimer's dementia includes acetylcholinesterase inhibitors (donepezil, rivastigmine and galantamine) and a NMDA receptor antagonist (memantine for moderate to severe Alzheimer's disease). These medications have shown to have an effect on some cognitive and non cognitive symptoms of the pathology. However, their efficacy remains limited and may decrease with time. There is an unmet medical need in this pathology. Masitinib is a selective tyrosine kinase inhibitor that is thought to exert a neuroprotective effect through its activity on mast cells and other non-neuronal cells of the central nervous system, with subsequent modulation of inflammatory and neurodegenerative processes, as well as possibly disruption of the Aβ signaling cascade via inhibition of the Fyn signaling pathway. This is a multicenter, double-blind, randomized, placebo-controlled, parallel-group study of oral masitinib. The objective of this study is to compare the efficacy and safety of masitinib at various doses versus matched placebo in the treatment of patients with mild to moderate Alzheimer's Disease. Masitinib will be administered as add-on therapy in patients who have been treated for a minimum of 6 months with a stable dose of cholinesterase inhibitor (donepezil, rivastigmine or galantamine) and/or memantine. Approximately 675 patients will be randomized into 5 treatment groups. The co-primary outcome measures are the Alzheimer's Disease Cooperative Study Activities of Daily Living score (ADCS-ADL), and Alzheimer's Disease Assessment Scale-Cognitive Subscale score (ADAS-Cog) after 24 weeks of treatment.

Inclusion criteria include:

1. Patient with dementia of Alzheimer's type, according to the Diagnostic and Statistical Manual of Mental Disorders criteria (DSM-IV)
2. Patient with probable Alzheimer' disease according to the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association criteria (NINCDS-ADRDA)
3. Patient with MMSE ≥ 12 and ≤ 25 at baseline
4. Patient treated for a minimum of 6 months with a stable dose of cholinesterase inhibitors (donepezil, rivastigmine or galantamine) at baseline, and/or a stable dose of memantine for a minimum of 6 months at baseline, with no changes foreseen in therapy throughout the study.

Exclusion criteria include:

1. Patient with any other cause of dementia not due to Alzheimer's disease.
2. Patient with Alzheimer disease with severe forms of delusions or delirium (patients with light and mild forms of delusions and delirium will be allowed in the study).