Langerhans cell histiocytosis and Erdheim‐Chester disease,both with cutaneous presentations,and papillary thyroid carcinoma all harboring the BRAFV600E mutation

Langerhans cell histocytosis (LCH) and Erdheim‐Chester disease are two rare histiocytic disorders. Their occurrence in the same patient is more infrequent, but has been described. We report a case of a 38‐year‐old woman who presented with a diagnosis of single system cutaneous LCH. Subsequently, she developed multiple papules on her extremities consistent with a non‐LCH xanthogranuloma type lesion. BRAF^V600E mutation immunostain, VE1 was positive in the skin lesion, which was confirmed by molecular polymerase chain reaction (PCR) studies, initiating a complete systemic workup for Erdheim‐Chester disease. Systemic involvement was confirmed with bilateral sclerotic bone lesions and retroperitoneal and pelvic fibrosing disease. She was also found to have a BRAF^V600E mutation positive papillary thyroid carcinoma. New suspicious cutaneous lesions presenting in patients with a history of LCH need to be biopsied. A BRAF^V600E mutation in a non‐LCH histiocytic lesion with a xanthogranuloma phenotype (CD163/CD68/CD14/fascin/Factor 13a) should prompt an Erdheim‐Chester disease workup. This is a unique case of a woman with BRAF^V600E mutation positive Erdheim‐Chester disease and cutaneous LCH, while also being, to our knowledge, the first reported case in the English literature of it occurring in a patient with a BRAF^V600E mutation positive papillary thyroid carcinoma.