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Langerhans' cell histiocytosis mimicking metastatic carcinoma of the lung

Langerhans' cell histiocytosis (LCH), previously known as Histiocytosis X, is characterized by abnormal accumulations of large mononuclear cells forming granulomas in various organs, mainly bone, skin and lung. This case report describes a 50‐year‐old man with a history of left pneumonectomy due to squamous cell carcinoma (SCC). During routine follow up, a CXR showed new parenchymal nodules in the right lung 57 months post treatment. Chest CT scan confirmed the presence of multiple parenchymal nodules. Open lung biopsy from the right upper lobe was performed and LCH was diagnosed. Re‐analysis of the initial pneumonectomy specimen revealed no evidence of LCH in the surrounding lung tissue. On diagnosis, the patient stopped smoking and was treated with vinblastine and prednisolone for LCH. The nodules disappeared and have not returned in a further 18 months of follow up. In this patient LCH was diagnosed after SCC, which highlights that smoking‐related diseases can be seen concomitantly or sequentially in the same patient.