Indomethacin is an effective treatment in adults and children with bone Langerhans cell histiocytosis (LCH)

Langerhans cell histiocytosis (LCH) is a rare disease due to a clonal proliferation of myeloid precursors that differentiate in CD1a+/CD207+ in lesions. More frequent in children than in adults, it can occur at any age with various degrees of systemic involvement. Among the large landscape of clinical manifestations, bone involvement represents the commonest single organ involved in LCH. Many different therapeutic strategies have been used for bone LCH.1, 2 Among less toxic and more effective regimens, indomethacin was found to be an effective analgesic and, subsequently, its effectiveness in reversing the disease process in children with symptomatic bone LCH, at diagnosis, or after reactivation, was demonstrated.3-5 The rationale of its use is based on the mechanism of action of indomethacin, a non‐steroidal anti‐inflammatory drug that inhibits the cyclooxygenase 1 and 2 enzymes, involved in the arachidonic acid–prostaglandin pathway. Prostaglandins (PGs), the hormone‐like molecules derived from arachidonic acid, have been implicated in the pathogenesis of LCH.6, 7 In our centre, we first successfully employed indomethacin as salvage therapy in LCH patients with multiple bone reactivations, including those with other organ or tissue involvement.8 We then used indomethacin as first‐line treatment in patients with unifocal or multifocal bone LCH, trying to avoid the potential toxicity of traditional therapy