P544: single-system unifocal adult langerhans cell histiocytosis: a single-center retrospective study

Background: Langerhans cell histiocytosis (LCH) is a rare highly heterogeneous histiocytosis, which can be divided into single system(SS) and multiple system(MS) according to clinical site of involvement. There are few studies related to single-system unifocal adult LCH currently. Aims: Objective of this single-center retrospective study is to describe the clinical features, affected organs, gene mutations, treatment and prognosis of adult single-system unifocal LCH patients. Methods: This retrospective study included patients ≥14 years old, and diagnosed with single-system unifocal LCH in Peking Union Medical College Hospital (Beijing, China) from September 2001 to December 2022. Results: Overall 109 patients were enrolled in this study, with a 2.03:1 male to female ratio. Median age at diagnosis was 33 years (14-69). The most common clinical manifestations were bone pain, accounting for 30.3%, followed by cough (11.0%) and diabetes insipidus (11.0%). The most common organs involved were bone (53.2%), followed by lung (18.3%), pituitary (10.1%), lymph nodes (5.5%), skin (2.8%), liver (2.8%) and thyroid (0.9%). Among the 20 patients with lung involvement, 17 patients had smoking history. The frequency of BRAFV600E mutation, MAP2K1 mutation and BRAFindel mutation were 24.3%, 10.8% and 2.7% respectively. BRAFV600Emutations and MAP2K1 mutations were independent of the type of organ involved and were not associated with OS and PFS. As for first-line treatment, 48 had surgery, 15 had radiotherapy, 16 were suggested observation, 9 had chemotherapy. All of the 20 patients with lung involvement were suggested to quit smoking. After a median follow-up time of 43.2 months (0.2-246.6), 3 patients died of respiratory failure, and the estimated 3-year overall survival (OS) was 98.7%. 24 patients developed disease progression, of which 5 had local recurrence, 4 progressed to single system multiple lesions (SS-M) and 15 progressed to MS, and the estimated 3-year progression-free survival (PFS) was 79.0%. Progression rate of pituitary involvement was the highest, 45.5% (5/11), followed by lymph node 33.3% (2/6), lung 20.0% (4/20) and bone 19.0% (11/58) (Figure 1). Univariate analysis showed that patients whose age at diagnosis ≤30 years had significant shorter PFS than those older than 30 years (the estimated 3-year PFS 89.1% vs 66.9%, p =0.039). Summary/Conclusion: In this study, we report a large series of single-system unifocal adult LCH patients. Bone is the most commonly involved organ. The overall survival of single-system unifocal adult LCH is good，and more than 30 years at diagnosis indicate good PFS.Figure1: Progression pattern of each affected organ（N=106） Keywords: Adult, Langerhans Cell Histiocytosis