Adult Langerhans cell histiocytosis with thyroid gland involvement: clinical presentation, genomic analysis, and outcome.

The present study aims to evaluate the characteristics and treatment outcomes of adult Langerhans cell histiocytosis (LCH) patients with thyroid involvement. We retrospectively described the clinical, biological, and genomic characteristics of a series of 36 LCH patients with thyroid involvement in our center between January 2001 and December 2021. At the time of diagnosis, only one patient was classified as having single-system LCH, and 35 patients were classified as having multisystem (MS) LCH. Three patients had coexisting papillary thyroid carcinoma. Patients with thyroid gland involvement had higher frequencies of pituitary (88.6% vs. 53.4%, P < 0.001), liver (45.7% vs. 20.7%, P = 0.003), and lymph node (54.3% vs. 31.6%, P = 0.012) involvement and a lower frequency of bone (45.7% vs. 72.0%, P = 0.003) involvement than patients without thyroid gland involvement. Sixteen patients had abnormal thyroid function, including nine patients with primary hypothyroidism, one patient with central hypothyroidism, and six patients with subclinical hypothyroidism. BRAF, BRAF , and MAP2K1 mutations were detected in 14.3%, 57.1%, and 7.1% of patients, respectively. After a 43-month median follow-up, none of the patients died, and 15 patients experienced reactivation. The median event-free survival was 37.5 months. Two of 6 patients with subclinical hypothyroidism had normal thyroid function, and 12 patients still had hypothyroidism after treatment. As the largest adult LCH cohort with thyroid gland involvement to date, we found that patients with thyroid gland involvement had different clinical characteristics, genetic profiles, and outcomes than patients without thyroid gland involvement.