Classification

The classification of ALL has followed the historical evolution of technology, with cellular morphology by microscopic appearance, immunophenotyping of cell surface markers, lymphocyte subset analysis, and more recently, chromosome evaluation and genomic identification.

Leukemia was first identified and described by Virchow as weisses blut (white blood) due to hyper-leukocytosis (elevated white blood cell count), and was further categorized initially using supravital stains of peripheral blood.47 Subsequent identification of leukemias by cell origin, required separation into groups of myeloid and lymphoid leukemias. Additionally, the identification of acute and chronic varieties of each required more sophisticated techniques of special enzymatic stains, leading to the evolution of our current skills in morphology, cell surface identifications, genomics, and biology as incorporated in the current World Health Organization (WHO) classification.48

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