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.