Erdheim–Chester disease: description of two illustrative cases involving the lung

Aim: Erdheim–Chester disease represents a clonal systemic proliferation of histiocytes. Bone is the most common site of involvement, although almost any organ, including the lungs, can be affected. Methods and results: The diagnosis of Erdheim–Chester disease can be difficult, owing to its rarity and protean presentation. Correlation between clinical, radiological and histological findings is mandatory for identification of the disease. Foamy histiocytes, lacking Langerhans cell markers, represent the typical histological findings, although their absence does not rule out Erdheim–Chester disease. Identification of BRAF mutation can be helpful in making the diagnosis, and allows for the development and application of targeted therapies in this setting. Conclusions: Herein, we describe two cases presenting with lung involvement and vertebral lesions, lacking the more typical long-bone involvement. One case histologically mimicked Rosai–Dorfman disease. However, both cases harboured the pathognomonic BRAFV600E mutation.