BRAF V600E–Mutant Diffuse Pulmonary Langerhans Cell Histiocytosis Successfully Treated With Dabrafenib Plus Trametinib: A Case Report

Pulmonary Langerhans cell histiocytosis (PLCH) is a rare diffuse lung disease that is strongly associated with cigarette smoking, with the BRAF V600E mutation identified in approximately half of all cases. In Japan, combination therapy with BRAF and MEK inhibitors has recently been approved as an alternative treatment option. We report the case of a 30‐year‐old woman diagnosed with BRAF V600E–mutant PLCH who was treated with dabrafenib in combination with trametinib. Chest computed tomography performed 3 months after the initiation of therapy demonstrated improvement in pericystic opacities, and this radiological response was sustained for over 1 year. Improvements in exercise tolerance, pulmonary function, and pulmonary haemodynamics have been observed clinically. These findings suggest that dabrafenib plus trametinib is a promising therapeutic option for patients with PLCH.