A 78-year-old Japanese woman noticed a subcutaneous nodule on her neck. On physical examination, we found a reddish tumor, measuring 25×20 mm, on her neck and multiple small nodules on her chest and back (Fig. 1A). There were no enlarged lymph nodes. Her white blood cell count was normal, and other routine biochemical tests also yielded normal results. The bone marrow aspiration sample showed no evidence of increased blast cell count. Computed tomographic scan of the whole body showed no lymphadenopathy. Histopathological examination of tumor in the neck showed diffuse infiltration of histiocyte-like tumor cells with remarkable dyskaryosis in the dermis (Fig. 1B, C). Immunohistochemical studies revealed that tumor cells were positive for leukocyte common antigen, CD43, CD56, CD68 (Fig. 1D), and myeloperoxidase (MPO) (Fig. 1E) and negative for keratin, terminal deoxynucleotidyl transferase, CD34, c-kit, CD3, CD4, CD5, CD7, CD8, CD20, CD21, CD138, granzyme B, S-100, and CD1a. Based on these findings, the diagnosis of primary granulocytic sarcoma (GS) without hematologic involvement was established. Patient was administered local irradiation (total, 30 Gy) and chemotherapy with etoposide. After 1 cycle of chemotherapy, the skin tumor on her neck regressed. During 5-week follow-up period, she did not develop acute myeloid leukemia (AML).

GS is manifested as a tumor at the extramedullary site and consists of immature granulocytes. The skin lesions of GS are generally manifested as papules, nodules, tumors, or plaques. GS occurs in only 3% to 8% of leukemia patients and is often associated with AML and chronic myeloproliferative disorder1,2. GS can occur in one of the following 3 patterns: (1) with AML or other bone marrow and blood involvement, (2) as an isolated recurrence of AML or as a sign of blast transformation in patients with chronic myeloid leukemia or myeloid dysplasia, (3) before the development of systemic leukemia, as a harbinger of AML3. Primary GS in the absence of any past history of leukemia is rarely reported1,2,3,4; in these cases, systemic leukemia developed after the emergence of primary GS3.

Primary GS without hematologic disorders is commonly misdiagnosed as lymphoma or histiocytic, lymphoblastic, or lymphocytic leukemia. One study stated that the rate of misdiagnosis was 46% (71/154 cases)5. Therefore, immunohistochemical analysis should be performed to arrive at a correct diagnosis. MPO is the marker of myeloid lineage and is a useful marker of GS. Antibodies to lysozyme and chloroacetate esterase can also be used to arrive at a diagnosis. CD68 positivity of the tumor cells indicates that they are monocytic and of granulocytic lineage.

The prognosis of GS is poor, especially when associated with AML3. Byrd et al.5 stated that 97% of all primary GS patients who did not receive systemic chemotherapy later developed AML. Furthermore, 66% of the patients who received chemotherapy for the primary GS never developed AML5, suggesting that early systemic therapy is helpful in preventing AML development and increasing the overall survival5. Therefore, establishing an early, correct diagnosis and administering appropriate treatment are important aspects that dermatologists and hematologists need to bear in mind.