We performed a retrospective analysis of 32 cases of extramedullary myeloid tumour in patients aged 11 weeks – 85 years (median 26 years), identified from the records of the Addenbrooke’s Hospital Department of Pathology over a 10 year period from 1st January 1997 to 15th January 2007. Records were reviewed for diagnosis, immunohistochemical stains, demographics, clinical and radiological features, treatment and outcome. 9 patients (28%) had a pre-existing haematological disorder, 6 (19%) presented with simultaneous EMMT and leukaemia, and 17 cases (53%) with de novo isolated EMMT. The most commonly positive immunohistochemical stains were CD43 (100%), CD45 (95%), CD68-PGM1 (91%), MPO (83%), CD 15 (78%) and CAE (73%). None of the 26 cases tested was positive for CD3, cytokeratin was negative in all tested patients, two cases were positive for CD79a, 9 of 9 cases were strongly positive for MIB1, 6 of 6 were positive for bcl-2, and vimentin positive in 3 of 3 cases. Misdiagnosis occurred in 10 out of the 17(59%) isolated de novo presentations. These were thought to be lymphoma (6/10), sarcoma (1/10), plasmacytoma (1/10), rhabdomyosarcoma (1/10) and fibromyomatosis (1/10). All the bcl-2 positive cases were misdiagnosed as non-Hodgkin’s lymphoma, even in the absence of specific B- or T-cell markers, and 1 vimentin positive case as sarcoma. No misdiagnosed case was initially tested for chloroacetate esterase or myeloperoxidase, in 9 subsequent testing showed one or both to be positive. 9 of 32 cases were (28%) long term survivors with a median follow up 1610 days, 7 adults and 2 children. Two received local therapy only with excision and radiotherapy, all others received intensive AML chemotherapy. There was only 1 long term survivor of the 6 patients initially given non-AML chemotherapy as a result of misdiagnosis. In that patient the diagnosis was revised within 14 days. All other misdiagnosed patients treated with non AML chemotherapy progressed to AML and were unsalvageable. Isolated EMMT may give rise to significant diagnostic difficulty. These tumours are usually positive for CD45, MPO and CAE but unless these are tested for, isolated expression of vimentin and bcl-2 may be misleading. In our series outcome was adversely affected by diagnostic delay, initial non-AML therapy, lymphadenopathy and tumour bulk (>10cm) at diagnosis. In correctly diagnosed patients AML chemotherapy alone may be sufficient to achieve long-term disease free survival in contrast to other recently published studies.
Disclosure: No relevant conflicts of interest to declare.