It has been recognized for many decades that epithelial dysplasia can represent an early histological sign of epithelial neoplasia. So it is with hematopoietic tissue wherein dysplasia of bone marrow cells can be an early sign of impending acute myeloid leukemia. Although this 'preleukemic syndrome' of hematopoietic dysplasia can often be identified well in advance of the classic histological signs of acute leukemia, a wide variety of basic studies on bone marrow cells, from patients and from experimental animals with induced preleukemia, clearly indicate that the preleukemic marrow cells are members of a fully established neoplastic clone. Consequently, it is likely that the preleukemic syndrome is merely acute leukemia diagnosed earlier than usual and which, in some patients, can be very slowly progressive, and in others may not progress at all. This article reviews the evidence in support of the notion that the preleukemic syndrome is an 'early leukemia', places the preleukemic syndrome in the context of a larger group of myelodysplastic disorders, reviews the laboratory studies of value for both diagnosis and for use in the assessment of prognosis, and summarizes the therapeutic options available for the management of patients with this disorder.
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