 The study we propose is a pilot phase II, interventional, treatment, open-label, single-arm, efficacysafety clinical trial of a 6-month treatment with tocilizumab 8 mgkg once monthly in adult patients with extraskeletal Erdheim-Chester disease ECD. Efficacy will be assessed as the effect of the treatment on the size of the measurable lesions, as evaluated by bidimensional measurements, and by the impact of the treatment on symptom control and on patient quality of life. Safety of the treatment will be determined by the analysis of adverse events and of the relevant safety laboratory parameters. 