Bone pain due to fibrous dysplasia of bone is usually treated with bisphosphonates. A small
proportion of patients fail to respond adequately. Mutated bone cells produce large amounts
of Interleukin-6 (IL-6), with increased bone resorption as a result. Inhibition of IL-6 may
be of interest to reduce bone resorption and therefore bone pain. TOCIDYS is a
placebo-controlled randomized cross-over trial to test the hypothesis that tocilizumab can
reduce bone resorption in those patients with fibrous dysplasia who have already received
bisphosphonates.