Acute myeloid leukaemia and myelodysplastic syndromes with 50% or greater erythroblasts: a diagnostic conundrum.

Acute myeloid leukaemia (AML) and myelodysplastic syndromes (MDS) with ≥50% erythroblasts comprise up to 5% of all cases of AML and 15% of MDS. The classification of these entities is currently fraught with difficulty and requires integration of clinical, morphological and cytogenetic features. The current World Health Organization classification of haematopoietic tumours recognises the entities of pure erythroid leukaemia and acute erythroid leukaemia (erythroid/myeloid), however, some cases of AML with erythroid predominance may also fulfil criteria for AML with myelodysplasia-related changes or therapy-related myeloid neoplasms. Among these entities, pure erythroid leukaemia remains poorly characterised due to its rarity. In addition, there is significant clinicopathological overlap between acute erythroid leukaemia and cases of MDS with ≥50% erythroblasts. In this review, we discuss current areas of controversy regarding these disorders and present our approach to their diagnosis and classification.