Masitinib in Severe Indolent or Smoldering Systemic Mastocytosis Unresponsive to Optimal Symptomatic Treatment

Inclusion Criteria:

1. Patient with one of the following documented mastocytosis subtypes (variants):Smouldering Systemic Mastocytosis, Indolent Systemic Mastocytosis
2. An excess of mast cells or a presence of abnormal mast cells in at least two organs (among skin, bone-marrow and GI Tract).
3. Patient with documented systemic mastocytosis and evaluable disease based uponhistological criteria
4. Patient with documented treatment failure of his/her symptom(s) (within the past 2years) with at least two of the symptomatic treatments used at optimized dose: AntiH1, Anti H2, Proton pump inhibitor, Antidepressants, Cromoglycate Sodium,Antileukotriene.
5. Patient with severe symptoms of mastocytosis over the 14-day run-in period includingat least one among pruritus, flushes, and depression: pruritus score ≥ 9, number offlushes per week ≥ 8, Hamilton rating scale for depression (HAMD-17) score ≥ 19.

Exclusion Criteria:

1. Patient with one of the following mastocytosis: Cutaneous Mastocytosis, SystemicMastocytosis with an Associated clonal Hematologic Non Mast cell lineage Disease (SM-AHNMD), Mast cell leukemia (MCL), Aggressive systemic mastocytosis (ASM)
2. Previous treatment with any Tyrosine Kinase Inhibitor
3. Treatment with any investigational agent within 8 weeks prior to screening.