Interest of Denosumab Treatment in Osteoporosis Associated to Systemic Mastocytosis

Inclusion Criteria: * Male or female \>/= 18 years of age at time of informed consent * Willingness and ability to sign informed consent, comply with scheduled visits, treatment plan, laboratory tests and other study procedures. * Patient with Indolent systemic or cutaneous mastocytosis according to WHO criteria (Appendix 4) with any specific treatment including corticosteroid, chemotherapy and immunomodulating drugs. * Patient with: * osteoporosis defined as bone mineral density T score ≤ -2.5 at the lumbar spine, OR * osteopenia defined as BMD T-score \>-2,5 and ≤ -1 at the lumbar spine and low energy fracture (defined as fractures that are associated with decreased bone mineral density. Are excluded fractures of skull, face, mandible, metacarpals, fingers, or toes, pathologic fracture, and fracture that are associated with severe trauma). (in case of osteoarthritis at the lumbar spine, the T score at left femoral neck or total left hip can be used to define osteoporosis or osteopenia) Exclusion Criteria: * Patient with aggressive mastocytosis or/and Associated Hematologic Non-Mastocytosis Disease (AHNMD) * Patient with conditions that influence bone metabolism (primitive hyperparathyroidism, hyperaldosteronism, hypercorticism, etc …) * Patient treated with intravenous bisphosphonate within 1 year prior to enrolment or with any other antiosteoporotic treatment within 3 months before enrolment. (per os bisphosphonate, strontium ranelate) Calcium and vitamin suppleme…