抄録
Myeloid sarcoma (MS) is a rare extramedullary tumor mass consisting of mature or immature myeloblasts. MS occurrence is mainly associated with the onset of acute myeloid leukemia (AML) and has a poor prognosis. MS also occurs, to a lesser extent, in myelodysplastic syndromes (MDS). The progression of MDS depends on the percentage of myeloblasts in peripheral blood or bone marrow. The transformation to AML is defined as the presence of more than 20% of myeloblasts. Herein, we report an extremely rare case of intraoral MS that arose in the hard palate over the course of the leukemic transformation of MDS. A 72 years-old Japanese man with a medical history of MDS was referred to our department because of continuous bleeding from the teeth extraction sockets. He had a gingival mass resembling a palatal abscess in his hard palate and underwent tooth extraction and puncture of the mass. Blood tests revealed that the proportion of myeloblasts increased up to 9% at that time. An incisional biopsy was carried out. Analysis of the histopathological findings showed aggregation of large, blast-like cells under the gingiva. These cells were positive for myeloperoxidase, naphthol AS-D chloroacetate esterase, CD68, and CD117 and negative for CD3, CD20, CD79a, and CD138. The Ki-67 labeling index was about 80%. The histopathological diagnosis was MS. Because stage progression of MDS was suspected, the hematologist performed bone marrow aspiration. The percentage of myeloblasts in the bone marrow was 26%, and the diagnosis of transformation to AML was confirmed. After one course of remission-induction chemotherapy by low-dose cytarabine, aclarubicin, and granulocyte-colony stimulating factor, the myeloblasts disappeared from the peripheral blood and bone marrow, the intraoral tumor regressed completely, and no further bleeding was observed. Twelve months after the chemotherapy, the patient died from a pneumonia.
