Correlative study of disease activity in Langerhans cell histiocytosis.

e19540 Background: Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasia that primarily affects younger children, most often involving bone, skin, lung, lymph nodes, or liver. Current treatment for LCH includes chemotherapy and biologically targeted therapies. Given its clinical heterogeneity and low prevalence, decision-making regarding intervention relies on subjective evaluation of disease status, which is often dependent on provider experience. Thus, there is a need to identify biomarkers for disease recurrence and activity in patients with LCH. Methods: We conducted a retrospective cohort study including pediatric LCH patients (n = 48) ≤21 years of age with biopsy-proven diagnosis of LCH and ≥1 year of follow-up after diagnosis. Data regarding demographics, symptom history, organ system involvement, and laboratory values at different time points were extracted from the from patient medical records and entered into a REDCap Database. The primary outcome was recurrence status as measured by the end of the study period. Data were analyzed using Stata statistical analysis software. Results: In our cohort, the sample was 64.6% Male and 35.4% Female with a median age of 29 months at diagnosis. 68.1% of patients had single organ involvement while 31.9% exhibited multi-system involvement. 70.8% of our cohort received treatment with chemotherapy with an average initial treatment duration of 12.1 months. 27.1% of the cohort experienced recurrence by the time of chart review. Logistic regression of the demographic factors and lab values at diagnosis revealed a statistically significant association between multi-system involvement (OR: 3.94, p = 0.04), moderate or high central nervous system risk assessment (OR: 7.67, p = 0.03; OR: 5.75, p = 0.03) and likelihood of recurrence. Additionally, logistic regression analysis revealed that alkaline phosphatase level at the time of diagnosis was associated with a slightly decreased likelihood of recurrence (OR: 0.987, p = 0.02). Conclusions: These results reveal that in addition to the traditionally utilized inflammatory markers (Erythrocyte Sedimentation Rate, White Blood Cell and Platelet Count), Alkaline Phosphatase could be used as a predictor of disease activity for patients with LCH, especially for those with bone involvement. Moving forward, an increased sample size might reveal other correlative biomarkers that can predict disease activity, helping to more precisely manage LCH.