We report an unusual diagnostic problem in a 35 year old woman with bilateral breast lumps. The patient first presented in August 1998 with a two week history of fever, tooth infection, and easy bruisability. Her full blood count showed severe pancytopenia (total white blood cell count, 1.0 × 10⁹/litre; neutrophil count, 0.1 × 10⁹/litre; haemoglobin, 66 g/litre; platelet count, 22 × 10⁹/litre). Her past medical history was unremarkable. She had no causative medications, chemical exposure, or viral symptoms. Flow cytometry for paroxysmal nocturnal haemoglobinuria was negative. A bone marrow biopsy showed a hypolastic marrow consistent with aplastic anaemia. She had no response to standard doses of antithymocyte globulin, methylprednisone, and cyclosporine and underwent a sex mismatched sibling allogeneic transplant. She had essentially no graft versus host disease, and five months after transplantation she did not return for follow up when all drugs were stopped.

In April 2004, she presented with bilateral breast lumps, nearly six years after transplantation. She had received a course of antibiotics six weeks previously for an indurated lesion in the right inframammary region. On examination, there were erythematous changes over both breasts, and in the left upper outer quadrant there was a hard mass. Enlarged nodes were palpable in both axillae. The subcutaneous mass in the right inframammary region was indurated, hyperpigmented, and ulcerated towards one edge.

Diagnostic investigations were carried out in the following sequence:

1. Fine needle aspiration cytology of the breast lesion showed a monomorphic population of neoplastic cells suspicious of a haemopoietic malignancy. Flow cytometry on this aspirate showed the expression of CD34, CD33, CD117, and CD4 on these cells.

2. The biopsy of the subcutaneous lesion (right inframammary region) showed a poorly differentiated malignancy expressing CD45, CD34, CD117, and CD4 (immunohistochemistry).

3. At presentation the blood counts were normal (haemoglobin, 160 g/litre; total white cell count, 8.6 × 10⁹/litre; platelet count, 192 × 10⁹/litre). The peripheral smear was unremarkable. The bone marrow was hypocellular with 16% blasts. These blasts were difficult to characterise by morphology or standard cytochemistry. Two weeks after admission, thrombocytopenia developed (haemoglobin, 150 g/litre; total white cell count, 9.9 × 10⁹/litre; platelet count, 130 × 10⁹/litre) and the blood film showed circulating blasts. A repeat bone marrow was hypercellular with 85% blasts. Flow cytometry confirmed a myeloid leukaemia with aberrant expression of CD4 as suggested by analysis of the breast aspirate. Fluorescent in situ hybridisation analysis showed that the tumour cells were XX (female), but with 15% residual male cells. Classic cytogenetics revealed a 46 XX, add(5)(p15) karyotype. A World Health Organisation classification of acute myeloid leukaemia (AML), minimally differentiated, was ascribed to this tumour.

The bilateral breast lesions in this patient raised the possibility of a primary breast carcinoma or a lymphoma in the post transplant setting. The diagnosis of acute leukaemia involving the breasts, soft tissue, and subsequently evident in the bone marrow required multiple diagnostic tissue sampling and techniques. Although the first bone marrow suggested an evolving acute leukaemia with 16% blasts, the World Health Organisation criteria for acute leukaemia were not fulfilled. A second bone marrow taken two weeks later confirmed the diagnosis of AML.

Several studies have shown that longterm survivors of acquired aplastic anaemia may be at high risk for malignant disease. The overall 15 year cumulative incidence for any cancer was found to be 10.9% in an analysis of longterm outcome after allogeneic transplant for aplastic anaemia.¹ In another study, the incidence of myelodysplastic syndrome or leukaemias/lymphomas was higher in patients receiving immunosuppressive treatment compared with those undergoing allogeneic bone marrow transplantion, with solid tumours being common in these last patients.² AML presenting as a breast mass (chloroma, granulocytic sarcoma) is rare.³ There are only a few case reports of AML in the breast antedating AML in the bone marrow.⁴ However, to the best of our knowledge, there are no reports of such an occurrence in a post transplant patient.