Cutaneous myelofibrosis with JAK2 V617F mutation: metastasis, not merely extramedullary hematopoiesis!

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm. There are 31 reported cases of cutaneous involvement by PMF, most of which have been described as "extramedullary hematopoiesis." We report a new case of cutaneous involvement by PMF and demonstrate mutation of the Janus kinase 2 gene in the cutaneous lesions. Extramedullary myelofibrosis is best considered a metastatic phenomenon. Reporting such cases as extramedullary hematopoiesis may cause confusion with reactive forms of extramedullary hematopoiesis.