Coexisting BRAF-Mutated Langerhans Cell Histiocytosis and Primary Myelofibrosis with Shared JAK2 Mutation

Langerhans cell histiocytosis (LCH) is an infrequent disease, characterized by oligoclonal proliferation of immature myeloid-derived cells. However, the exact pathogenesis remains unknown. In rare cases, LCH is present in patients with concomitant myeloid proliferative neoplasms. Here, we describe a 69-year-old male, who presented with a maculopapular rash covering truncus, face, and scalp. A cutaneous ulcerating lesion on the right cheek led to a biopsy showing LCH. Lesional cells were BRAF(V600E) and JAK2(V617F) mutated. A bone marrow aspirate showed no infiltration of Langerhans cells, but alterations consistent with primary myelofibrosis (PMF) and a polymerase chain reaction test were positive for JAK2(V617F). Our case highlights an uncommon condition of two hematological malignancies present in the same patient. The identification of the BRAF(V600E) mutation supports previous findings of this mutation in LCH. Interestingly, a JAK2(V617F) mutation was found in both LCH and PMF cells, indicating a possible clonal relationship between the two malignancies.