Multiple facial neoplasms in a pediatric patient during treatment for B-lymphoblastic leukemia/lymphoma.

Histiocytoses encompass a group of rare mononuclear phagocytic cell proliferations with diverse presentations and overlapping features, making them at times difficult to classify. We present a unique case of one such histiocytic disorder, juvenile xanthogranuloma (JXG), in a 15-year-old patient who developed lesions shortly after initiation of chemotherapy for treatment of B-lymphoblastic leukemia/lymphoma and displayed genetic mutations not typically associated with JXG. Appropriate diagnosis and management of JXG requires an understanding of key features in clinical presentation and histopathology, associated conditions, and genetic mutations.