Primary myelofibrosis and extramedullary blastic transformation with hemophagocytosis.

which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. A 72-year-old woman presented with bleeding, swollen gums, and painful cervical lymphadenopathy. A CT scan revealed diffuse lymphadenopathy and hepatosplenomegaly. Initial laboratory tests showed the following: WBC level, 11.1 μg/mL; and a differential count with marked leukocytosis with a left shift. Bone marrow biopsy indicated prefibrotic myelofibrosis. There was no evidence of JAK2 or BCR/ABL mutation or Epstein-Barr virus load. Trisomy 8 mosaicism was detected (47, XY, +8[6]/46, XY[24]) on karyotyping. Excisional lymph node biopsy revealed immature myeloid cells admixed with mature myeloid components and occasional megakaryocytes (A: H&E, ×400). Most notably, there were numerous hemophagocytic macrophages (arrowheads). Blasts comprised 40% of the total cellularity and showed a mixture of strongly MPO-positive myeloblasts and MPO-negative, CD68-positive, and CD163-positive monoblastic cells. The patient was diagnosed with primary myelofibrosis and extramedullary blastic transformation (granulocytic sarcoma) with acute myelomonoblastic differentiation accompanied by hemophago-cytosis. Therefore, hydroxyurea chemotherapy was initiated. Hemophagocytosis can be seen in leukemic transformation of myelofibrosis.