DEnosumab for the Treatment of FIbrous Dysplasia/McCune-Albright Syndrome in Adults (DeFiD)

DEnosumab for the Treatment of FIbrous Dysplasia/McCune-Albright Syndrome in Adults (DeFiD): a Randomized Double-blind Placebo-controlled Trial

Fibrous Dysplasia/McCune-Albright syndrome (FD/MAS) is a rare disease, consisting of the replacement of normal bone tissue with fibrous tissue. FD lesions may be isolated in one or more bones or may be associated with endocrinopathies in McCune-Albright syndrome. Bone lesions constitute of weak bone tissue, leading to higher risk of fractures, pain and decreased quality of life. There is no cure for FD lesions and current therapies failed to soothe patients' complaints or to display any effect on progression of the lesions on imaging. However, the RANKL-inhibitor Denosumab demonstrated encouraging results in mouse models and in off-label clinical use, leading to clinical, biochemical and radiographical improvements.

Study's aim is to investigate whether 3-monthly Denosumab will improve the clinical, radiological and biochemical manifestations of FD bone lesions.

Eligible patients will be randomized to treatment with either subcutaneous Dmab 120mg or placebo at baseline and 3 months in a blinded fashion. At 6 months, after 2 injections, patients with pain score <4 will exit the study to discontinue study medication and proceed in usual care, while patients with pain score ≥4 or lesional growth will be offered Dmab 120 mg at 6 and 9 months in an open-label design.

Inclusion Criteria:

• Symptomatic patients with established diagnosis of FD/MAS and closed growth plates(>18 years)
• Pain in the region of an FD localization, not responding to adequate pain treatment and without mechanical component e.g. impending fracture
• Pain score from FD lesion for maximum or average pain on VAS ≥ 4
• Increased lesional activity defined as increased bone turnover markers (ALP, P1NP or CTX) or increased activity on Na[18F]-PET/CT or bone scintigraphy in at least one lesion
• Normal levels of calcium, parathyroid hormone and vitamin D (supplementation is allowed)
• Treated hypophosphatemia (defined as >0.7 at two separate measures)
• good dental health (last check within the last 12 months)

Exclusion Criteria:

• Active pregnancy wish, pregnancy or nursing
• Pain not related to FD
• Uncontrolled endocrine disease
• Untreated vitamin D deficiency, hypocalcemia or hypophosphatemia
• Previous use of bisphosphonates or Dmab < 6 months before inclusion ('6 months wash out')
• Previously reported severe side effects on Dmab
• Inability to fulfil study requirements
• Poor untreated dental health without intention to get treatment
• Treatment with other bone influencing drugs, such as high doses corticosteroids