-mutated histiocytosis of the skull lacking the expression of Langerhans cell markers.

Langerhans cell histiocytosis (LCH) is a rare condition affecting children more frequently than adults. LCH can involve any organ in the body and has a wide spectrum of clinical presentation from a single self-healing bone lesion to a multisystemic life-threatening disease. The diagnosis of LCH requires histology with compatible clinical and radiological findings. Positive immunochemistry for both CD1a and CD207 is required for a definitive diagnosis of LCH. The majority of LCH shares oncogenic mutation. We report the case of a 55-year-old adult who presented with a single lytic self-healing lesion of the skull, invading adjacent soft tissues. The histology and cytology were also typical of LCH, and tumor cells contained the mutation. However, histiocytes were negative for CD1a and CD207. We suggest that this case might be considered as LCH, despite its abnormal phenotype.
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