Clinical features and outcomes of adult Langerhans cell histiocytosis: a single-center experience.

Langerhans cell histiocytosis (LCH) is a clonally expanding neoplasm characterized by the accumulation of CD1a + CD207 + myeloid dendritic cells. As LCH is a rare disease and is presumed to mainly affect children, the clinical features and treatment outcomes of adult LCH have been poorly documented. We retrospectively reviewed 53 adult patients with LCH who were referred to the Institute of Medical Science, the University of Tokyo from 2005 to 2018. The median age at diagnosis was 42 years with a slight female predominance (57%). The time between onset and diagnosis varied among patients (median, 8 months; range, 0–144 months). In total, 40% of the patients had single organ involvement and 60% had multiple organ involvement. Overall, the most frequently affected organ was bone (62%), followed by the central nervous system (34%), and the lung (28%). Twenty-six patients required systemic treatment, and 25 patients underwent the Special C regimen. Twenty patients (80%) who underwent Special C regimen showed a partial response or better with favorable toxicity. All but one patient is still alive. Median progression-free survival has not been reached despite a median follow-up of 35.5 months. Immunohistochemistry revealed that 39% of patients were positive for BRAF-V600E, which was a lower proportion than in previous reports from North America and Europe.