The treatment of systemic mastocytosis has two main axes:

• Control of mast cell activation symptoms and
• The control of proliferation (accumulation) of mast cells.

There is no standard treatment and no treatment has a marketing authorization for the treatment of monoclonal indolent mastocytosis.

Mastocytosis is an orphan disease related to the accumulation and / or the proliferation of abnormal mast cells in different tissues.

In adults, a classic distinction is made between isolated cutaneous forms (10 to 15%) and systemic forms (85 to 90%).

The treatment of systemic mastocytosis has two main axes:

• Control of mast cell activation symptoms and
• The control of proliferation (accumulation) of mast cells.

There is no standard treatment and no treatment has a marketing authorization for the treatment of monoclonal indolent mastocytosis.

Inclusion Criteria:

1. Age > 18 years

2. Isolated Cutaneous mastocytosis or indolent systemic mastocytosis with associated skin lesions defined according to WHO criteria (and / or international standards for cutaneous mastocytosis)

3. Patient with at least one disability defined by the presence of the following symptoms assessed as moderate to severe:

   1. Cutaneous pruritus with score ≥ 5 on a VAS scale from 0 to 10
   2. Number of flushes / week ≥ 7

4. Skin KIT mutation known

5. Performance scale: OMS/ECOG ≤ 1

6. Woman and man of childbearing age* under effective contraception during all the treatment by hydroxychloroquine, until 8 months after its cessation

Exclusion Criteria:

• Non-symptomatic mastocytosis and / or without skin involvement
• Advanced Systemic mastocytosis
• History of ophthalmic disease and / or cardiac conduction disorders, in particular the prolongation of the QT interval as well as the risk factors for prolongation of the QT interval, such as heart disease (heart failure, myocardial infarction), pro-arrhythmic conditions (eg bradycardia <50 bpm), history of ventricular dysrhythmias, uncorrected hypokalemia and / or hypomagnesemia, concomitant treatment with interval prolonging agents QTagainst-indicating the use of hydroxychloroquine
• Treatment with citalopram, escitalopram, hydroxyzine, domperidone, piperaquine due to the increased risk of ventricular rhythm disorders, especially torsades de pointes
• Specific anti-tumor treatment (chemotherapy, radiotherapy) of less than 4 weeks before inclusion.
• Concomitant specific anti-mast cell treatment
• Contre-indication(s) to XYLOCAINE 10 mg/ml ADRENALINE 0,005 mg/ml, injectable solution: Known hypersensitivity to chlorhydrate de lidocaïne, to amide-type local anaesthetics or one of its excipients (sulfites), patients suffering from recurring porphyrias, coronary insufficiency, ventricular rhythm disorders, severe arterial hypertension, obstructive cardiomyopathy, hyperthyroidism.
• Inclusion in another trial with an experimental therapeutic molecule
• Change symptomatic treatment (including dosage) in the 4 weeks preceding the inclusion visit
• Moderate to severe renal or hepatic failure or diabetes
• History of organ transplant
• Inability to give informed consent
• Inability to undergo medical monitoring for geographical, social or psychic
• Patients with major surgery scheduled in the next two weeks screening
• Patient without health insurance
• Pregnancy, Breastfeeding
• Vulnerable Patient, defined as:
• Esperanzae survival < 6 months
• Patient with another uncontrolled severe disease
• Patient under juridical protection