LAUSR

7018 Background: Langerhans cell histiocytosis (LCH) is a rare histiocytic neoplasm driven by MAPK-ERK mutations in majority of patients. Contemporary data on treatments and outcomes in adult LCH are lacking. Hence, we undertook this study to analyze a large cohort of adult LCH patients. Methods: This was a retrospective study of adult (≥18 years) LCH patients seen at our institution between 1998 and 2018. Results: We included 186 patients with adult LCH (median age 43; 19-88), and 54% were females. 70% of patients were diagnosed after 2007. Common presenting symptoms were cough/dyspnea (30%), rash (17%), pain/swelling in head (17%), and diabetes insipidus (10%). 70 (38%) patients had multisystem LCH, 62 (33%) had isolated pulmonary LCH, and 35 (19%) had unifocal LCH. Common sites of involvement included lung (59%), bone (37%), skin (21%), and nervous system (16%). 121 (65%) were smokers; 48% of these had lung disease, while 52% had multisystem disease. 18 of 31 tested (58%) patients had BRAF-V600E mutation. Most common first-line treatment was smoking cessation in 24 patients, and led to an overall response rate (ORR) of 83% in pulmonary lesions. Radiation therapy was used in 11 patients, and led to an ORR 82%. Surgical resection of lesion was done in 23 patients, with relapses in 24%. Systemic therapies were used in 78 (42%) patients (Table). Most common first-line systemic therapy was cladribine with ORR of 78%. Vemurafenib was used in 3 patients with BRAF-V600E, leading to an ORR of 67% . After a median follow-up of 23 months (0-261), 21 patients had died. Of these, 10 died of progressive LCH. Median OS was not reached, and mean OS was 196 months. Conclusions: This is the largest contemporary series of adult LCH. It shows that diverse clinical spectrum, ranging from benign course to a progressive multisystem disease. Although smoking cessation was an effective treatment for pulmonary LCH, a large subset required systemic chemotherapy. [Table: see text]