Langerhans Cell Histiocytosis: A Population-based Study of Anatomical Distribution and Treatment Patterns.

Background: Langerhans cell histiocytosis (LCH) is a rare monoclonal histiocytic neoplasm. Little is known about clinical factors associated with LCH single- vs multi-system involvement at the time of diagnosis. Methods: Data on 1549 LCH patients diagnosed between years 2010 and 2018 were extracted from the Surveillance, Epidemiology and End Results Program. Patterns of single- vs multisystem involvement were examined using multivariable logistic regression analysis. Odd ratio (OR) and 95% confidence interval (CI) were reported. Results: 968 children and adolescents (0-19 years; median: 4 years) and 581 adults (≥20 years; median: 49 years) were included in the analysis. Multi-system LCH was reported for 30.9 % patients. Bone marrow (BM) (OR = 3.776; 95 %CI = 1.939-7.351; P < 0.001) and lymph node (LN) (OR = 3.274; 95 %CI = 1.443-7.427; P = 0.005) involvement were most commonly associated with multi-system LCH at the time of diagnosis; similar pattern was also observed in adult patients (OR = 17.780; 95 %CI = 6.469-48.867; P < 0.001 for BM LCH; and OR = 5.156; 95 %CI = 2.131-12.471; P < 0.001 for LN LCH). Among pediatric patients, craniofacial osseous LCH was more likely to be treated with surgery (OR = 2.822; 95 %CI = 1.199-6.639; P = 0.018) compared to skeletal lesions in other sites, whereas vertebral body LCH was less likely to be treated with surgery (OR = 0.175; 95 %CI = 0.058-0.527; P = 0.002). In pediatric patients with bone LCH, the non-white patients were less likely to be treated surgically compared to the white patients (OR = 0.470; 95 %CI = 0.272-0.812; P = 0.007). Conclusions: BM and LN LCH are associated with the highest risks of multi-system disease, which may require active surveillance. Furthermore, active attempts are needed to mitigate the racial disparity in surgery utilization in pediatric patients with skeletal LCH.