Sclerosing extramedullary hematopoietic tumor.

A 73-year-old woman presented with abdominal pain, weakness, and weight loss. Pertinent medical history included myelofibrosis, severe anemia, and lumpectomy for breast cancer. Computed tomography showed marked splenomegaly and numerous soft tissue masses in the mesentery. Excisional biopsy of the mass showed an encapsulated tumor with yellow-tan nodular growth pattern. Microscopically, the tumor was characterized by the presence of bizarre giant cells in background of prominent dense fibrous stroma. The atypical giant cells were positive for FVIII antibody staining. Many other cells were positive for CD43 antibody staining, indicating that the tumor was hematopoietic in nature, so-called sclerosing extramedullary hematopoietic tumor. Extramedullary hematopoiesis is a common phenomenon associated with severe anemia of any cause. When associated with myelofibrosis, however, it has different morphology from extramedullary hematopoiesis of the other causes. The significance of recognizing sclerosing extramedullary hematopoietic tumor is that it is often mistaken for sarcomas and other malignant neoplasms, especially when the clinical history is unknown.