Adult pulmonary Langerhans cell histiocytosis might consist of two distinct groups: isolated form and extrapulmonary recidivism type

BACKGROUND: Adult pulmonary Langerhans cell histiocytosis (PLCH) is a rare form of Langerhans cell histiocytosis (LCH) that typically occurs in cigarette smokers. The clinical course of PLCH is unpredictable; the disease may resolve spontaneously, or lead to multi-organ failure and death. To better understand this idiopathic disease, we retrospectively overviewed a cohort of Asian patients with PLCHs. METHODS: Herein, we have provided detailed clinicopathological features and molecular findings of PLCHs in a Southwestern Chinese population, including the expressions of apoptotic protein P16, programmed cell death 1 (PD-1), and programmed cell death-ligand 1 (PD-L1). Importantly, the BRAF(V600E) mutation was observed in this cohort. RESULTS: In accordance with the follow up data, the cohort was subdivided into two groups, an isolated pulmonary group and extrapulmonary recidivism group. Among the isolated group, the participants were predominantly young males (<40 years old), with a history of smoking, respiratory symptoms (cough and difficulty breathing), showed more cystic lesions in computed tomography (CT) scanning, had more cellular Langerhans granulomas under the microscope, overexpression of P16 (66.7%), high PD-1 (100%) and low PD-L1 (33.3%) expressions, and no BRAF(V600E) mutation was detected. In contrast, the extrapulmonary recidivism group showed significantly older age (>40 years old), recurrent spontaneous pneumothorax, more nodular changes in CT scanning, more interstitial fibrosis histologically, expression rates of 100% of P16, 66.7% of PD-1, and 33.3% of PD-L1; and importantly, BRAF(V600E) mutation was detected in 33.3% of this subdivision. CONCLUSIONS: We found that adult PLCH might consist of two distinct groups: an isolated form and extrapulmonary recidivism PLCH. Overexpression of P16 could be a diagnostic biomarker for PLCH. An extremely low mutation rate of the BRAF gene in adult PLCH in our cohort indicated that there might be other pathogeneses for this disease among Asian patients.