Clinical features, genomic profiling, and outcomes of adult patients with unifocal Langerhans cell histiocytosis

BACKGROUND: Langerhans cell histiocytosis (LCH) is a rare highly heterogeneous histiocytosis, which can be divided into single system and multiple system disease according to site of involvement. There is a paucity of studies examining unifocal LCH in adults in the molecular era. RESULTS: We retrospectively analysed records from 70 patients with unifocal LCH. The median age at diagnosis was 36 years (18–69). The most common organ involved was the bone (70.0%), followed by pituitary gland (7.1%). Target gene sequencing of lesion tissues was performed on 32 of the 70 patients. MAPK/PI3K pathway alterations were observed in 78.1% of the patients; the most common mutations included BRAF(V600E) (28.1%), MAP2K1 (18.8%) and PIK3CA (9.4%). After a median follow-up time of 39.4 months (0.7–211.8), 10 (14.3%) patients developed disease progression, of whom 4 had local recurrence, 2 progressed to single-system multifocal and 4 progressed to multiple system LCH. The 3-year progression-free survival (PFS) was 81.9%. Univariate analysis showed that age < 30 years at diagnosis was associated with worse 3-year PFS (52.2% vs. 97.0%, p = 0.005). The 3-year overall survival was 100%. CONCLUSIONS: In our large cohort of adults with unifocal LCH, we found that prognosis of unifocal LCH in adults was very good, and age < 30 years at diagnosis was associated with increased relapse risk. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13023-023-02989-8.