A 47-year-old female presented with high-risk myelodysplastic syndrome (MDS) without detectable cytogenetic abnormality from the bone marrow specimen. Initially, she received azacytidine while awaiting bone marrow transplantation (BMT). After successful allogeneic BMT from a mismatched related donor, she received post-transplant care including management of transplant-related toxicity and skin manifestations of graft versus host disease (GVHD) in a designated BMT center. Subsequent bone marrow showed no evidence of MDS, and she is currently free from GVHD.

Approximately 1.5 years after BMT, the patient detected a palpable nodule in her right breast, just below the skin. Mammogram was negative. The lesion slowly enlarged over the next eight months, associated with brown skin discoloration. Breast ultrasound detected a 9-mm superficial mass with mixed echogenicity. Around the same time she found two hard lumps with similar skin color changes on the left and one on the right thighs. The lesions from the right breast and left thigh soft tissues were completely excised, while the right thigh mass was not excised, to be used as an index lesion to observe the effect of systemic therapy.

The hematoxylin and eosin stained sections demonstrated infiltration of the dermis and subcutaneous soft tissues by aggregates of medium to large cells that had finely dispersed chromatin (Figure 1A-B). These cells stained strongly positive for myeloperoxidase (Figure 2A), CD 43 (Figure 2B), CD68 and CD117 (Figure 2C). The neoplastic cells were negative for CD3, CD5, CD20, CD34, CD10, CD30, ALK1, CD138, kappa, lambda, CK7 and pan-cytokeratin. The morphology and immunohistochemistry findings support the diagnosis of myeloid sarcoma (also known as granulocytic sarcoma or chloroma). A subsequent bone marrow aspiration and biopsy did not reveal leukemic cells and cytogenetic studies were completely normal. PET scan did not detect overly hypermetabolic activity apart from subcutaneous soft tissue lesions in the left medial thigh with SUV of 2.2, corresponding to one of the excised lesions. The patient is currently undergoing chemotherapy intended for acute myeloid leukemia (AML).

Myeloid sarcoma is formed by immature myeloid cells and is considered a rare extramedullary manifestation of acute myeloid leukemia (AML). It can occur concurrently with, following or, rarely, preceding AML. It can also be seen in MDS or chronic myeloid leukemia. It was reported among 0.2–1.3% of patients following BMT [1]. The symptoms of myeloid sarcoma may vary dependent on its location, rate of growth and size. It is frequently misdiagnosed as lymphoma [2] or Ewing's sarcoma. The most common sites of myeloid sarcoma include subcutaneous soft tissue, bone, lymph nodes, and periosteum. Myeloid sarcoma in breast soft tissue is rare [3] with only isolated case reports following BMT. It is reported that MS may precede AML by 5–12 months [4]. Therefore, treatment using the same regime for AML is called for once the diagnosis of myeloid sarcoma is established.

As myeloid sarcoma in the breast soft tissue is very rare, it should be included in the differential diagnoses when a "breast lump" is found in a patient with non-lymphocytic hematological malignancy.

Keywords: Acute myeloid leukemia, Breast, Immunohistochemistry, Myeloid sarcoma

1. Szomor A, Passweg JR, Tichelli A, Hoffmann T, Speck B, Gratwohl A. Myeloid leukemia and myelodysplastic syndrome relapsing as granulocytic sarcoma (chloroma) after allogeneic bone marrow transplantation. Ann Hematol 1997 Nov-Dec;75(5-6):239–41.   [CrossRef]   [Pubmed]    
2. Byrd JC, Edenfield WJ, Shields DJ, Dawson NA. Extramedullary myeloid cell tumors in acute nonlymphocytic leukemia: A clinical review. J Clin Oncol 1995 Jul;13(7):1800–16.   [Pubmed]    
3. Valbuena JR, Admirand JH, Gualco G, Medeiros LJ. Myeloid sarcoma involving the breast. Arch Pathol Lab Med 2005 Jan;129(1):32–8.   [CrossRef]   [Pubmed]    
4. Tsimberidou AM, Kantarjian HM, Estey E, et al. Outcome in patients with nonleukemic granulocytic sarcoma treated with chemotherapy with or without radiotherapy. Leukemia 2003 Jun;17(6):1100–3.   [CrossRef]   [Pubmed]