A Case of Pulmonary Langerhans Cell Sarcoma Simultaneously Diagnosed with Cutaneous Langerhans Cell Histiocytosis Studied by Whole-Exome Sequencing.

Langerhans cell histiocytosis (LCH) and Langerhans cell sarcoma (LCS) are clonal proliferations of Langerhans-type cells. Unlike in LCH, the pathophysiology and clinical course of LCS are unclear due to its rarity. Here, we report the case of a 73-year-old male patient who was diagnosed with cutaneous LCH and pulmonary LCS at the same time. Pathological review of these 2 tumors revealed similar immunohistochemical findings. However, the tumor cells in LCS had more aggressive cytological features than those in LCH. Results of BRAF mutation analysis using real-time PCR were negative for both tumors. In whole-exome sequencing (WES), stop-gain mutations in TP53 gene were discovered only in LCS cells. The mechanism of development of LCS from various progenitor cells is currently unclear. According to the results of the WES study, changes in TP53 gene might have contributed to the malignant features of LCS.