Langerhans cell histiocytosis and Erdheim‐Chester disease, both with cutaneous presentations, and papillary thyroid carcinoma all harboring the BRAF V600E 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.