Participants and collection of samples

A retrospective study was conducted drawing from the archive of the West China Hospital of Sichuan University between January 2014 and December 2019. Due to the lack of demonstrable Langerhans cells in old fibrotic lesions, we selected 6 early (cellular) PLCH cases. All 6 adult PLCH participants had undergone fiberoptic bronchoscopic biopsy or surgical resection, followed by formalin-fixed paraffin-embedded (FFPE) tissue formation. All cases met the criteria of PLCH according to the 2015 World Health Organization (WHO) classification of tumors of the lung, pleura, thymus, and heart. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). Written informed consent was provided by all participants included in the analysis. This study was approved by the Ethical Committee of the West China Hospital (No. 2020-1211).

All clinical data were retrospectively collected from the database of the hospital information system, including symptoms and signs, smoking habits, history of present and past illness, laboratory examinations, chest computed tomography (CT) examinations and lung function tests, as well as any systemic treatments that had been administered. All participants were followed up, 3 cases were identified as PLCH accompanied by extrapulmonary involvement (extrapulmonary recidivism group, 3/6, 50%), and the others were allocated to the isolated pulmonary group (3/6, 50%).