An unusual myeloid sarcoma

Abstract

Myeloid sarcoma is a tumor mass of immature myeloid or monocytic cells (rarely erythroid or megakaryocytic) occurring in an extramedullary site. A de novo promyelocytic granulocytic sarcoma is a very rare tumor. We report a case of a young man presenting with a paraspinal myeloid sarcoma of promyelocytic origin.

Myeloid sarcoma is an uncommon tumor mass of immature myeloid or monocytic cells or rarely erythroid or megakaryocytic precursors occurring in an extramedullary site.¹ Myeloid sarcomas may occur de novo, may precede or coincide with acute myelocytic leukemia, or may represent a blast transformation of a preceding myelodysplastic disorder, myeloproliferative disorder, or myelodysplastic/myeloproliferative disorder. Almost any site in the body may be involved, but the most frequently involved areas are the skin, lymph nodes, gastrointestinal tract, soft tissue, and bone.² We report a rare case of a granulocytic sarcoma presenting as a de novo acute promyelocytic leukemia.

CASE DESCRIPTION

A 27-year-old man presented to the emergency department with back pain and leg numbness. Computed tomography of the spine revealed a paraspinal lumbar mass. He was admitted and underwent decompression laminectomy of L3 and semilaminectomies of L2 and L4 with an open biopsy. Pathology revealed a myeloid sarcoma composed of promyelocytes (Figure 1a). The cells stained positive for CD117 (Figure 1b), myeloperoxidase (Figure 1c), and CD33, and fluorescence in situ hybridization was positive for the PML/RARα fusion gene (Figure 1d). At the time of diagnosis, his hemogram revealed a white blood cell count of 3.5 × 10^3/μL, hemoglobin 8.5 g/dL, hematocrit 25.7%, and platelets 396 × 10³/μL. The differential was not remarkable as to the presence of abnormal cells. A bone marrow aspirate and biopsy were performed with no evidence of disease. He was started on treatment with the acute promyelocytic leukemia 4 protocol composed of all-trans-retinoic acid, idarubicin, and intravenous arsenic trioxide.³ The patient has been in remission for 10 months and is being treated and followed at another institution.

Figure 1.

(a) Hematoxylin and eosin sections of tumor, 40×; (b) CD117 positivity in tumor cells; (c) myeloperoxidase positive staining; (d) PML RARα scattered fluorescence in situ hybridization images showing fusion gene.

DISCUSSION

De novo acute promyelocytic granulocytic sarcoma is rare, with about 24 cases reported.⁴ Nine cases were without bone marrow disease at the onset, as was our case. Most of the cases developed bone marrow involvement within 1 to 16 months. With leukemic acute promyelocytic leukemia patients, myeloid sarcoma-extramedullary disease mostly occurs in the relapse stage, with the skin and central nervous system being the most common sites of involvement.^5,6 Nine of the de novo acute promyelocytic/myeloid sarcoma cases showed neural symptoms because of acute promyelocytic leukemia compression of the spinal cord, as did our case. The coagulation abnormality characteristic of acute promyelocytic leukemia was evident in only five cases and was not present in our case.

The diagnosis of extramedullary disease in association with acute promyelocytic leukemia seems to be more common following therapy with all-trans-retinoic acid rather than as the presenting sign.^7,8 It is hypothesized that all-trans-retinoic acid may predispose some patients to unusual forms of relapse due to prolonged survival. An ex vivo experiment showed that all-trans-retinoic acid increases adhesion molecules in leukemic cells, indicating the possibility of enhancing migration and adhesion to extramedullary tissues.⁹ In our case, however, the granulocytic sarcoma occurred de novo before any therapy was given.

In the isolated presentation of an extramedullary granulocytic sarcoma without any signs of leukemia, a misdiagnosis of a lymphoma or metastatic tumor may result. It is important that accurate histologic diagnosis be established to ensure proper treatment. Since the blood and bone marrow may be negative, the diagnosis must be made from the tissue biopsy. The use of appropriate immunohistochemical stains and fluorescence in situ hybridization for detection of the PML/RARα fusion gene led to the correct diagnosis of promyelocytic leukemia.

Since most previous cases of extramedullary acute promyelocytic leukemia were reported independently, the treatments differed. Most cases were treated with all-trans-retinoic acid with or without chemotherapy (daunorubicin and cytarabine) or a combination of all-trans-retinoic acid and arsenic trioxide. The acute promyelocytic leukemia 4 protocol as mentioned previously may also be utilized.