Myeloid sarcoma in essential thrombocythemia that transformed into acute myeloid leukemia.

A 72-year-old man was diagnosed with essential thrombocythemia (ET) and was treated with hydroxyurea for approximately 5 years. He was well until April 2007. In May 2007, a slight fall in hemoglobin levels was found. In June 2007, an upper endoscopy performed to investigate the cause of anemia showed multiple polypoid lesions in the body of the stomach. A gastric biopsy showed a diffuse infiltration of very immature cells. Several additional immunohistochemical staining showed that the cells were positive for CD13, CD34, CD117, and HLA DR, but negative for myeloperoxidase, CD42b, glycophorin, B cell marker, T cell marker, cytokeratin and desmin. We finally diagnosed the condition as myeloid sarcoma. Subsequently, the patient's ET transformed into acute myeloid leukemia. To our knowledge, this is an exceedingly rare event involving a patient with essential thrombocythemia.