A Case of Pulmonary Langerhans Cell Histiocytosis with BRAF V600E-negative and MAP2Kl-posivtive Mutations Presenting as Diffuse Nodules in Chest High-resolution Computed Tomography After Smoking Cessation

To the Editor： Pulmonary Langerhans cell histiocytosis （PLCH） in adults is a rare disease occurring almost exclusively in smokers. The characteristic high-resolution computed tomography （HRCT） manifestation of PLCH is a combination of cysts （or cavities） and nodules mainly in the upper lung zone. However, not all HRCT patterns of PLCH are typical. Few treatments are effective in current practice regarding PLCH. Targeted therapy with an inhibitor of mutated BRAF （vemurafenib） has been proved effective in Langerhans cell histiocytosis （LCH） harboring BRAF valine at position 600 （V600E） mutation.MAP2K1 mutations are mutually exclusive with BRAF mutations and might have implications for the use of BRAF targeted therapy. Here, we reported a case of PLCH proven by lung biopsy.