Both acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML), along with the other neoplastic blood disorders were originally classified by the French-American-British (FAB) system. The FAB classification system was based primarily on cell staging, cell morphology, and cytochemical staining. As genetic and chromosomal changes causing these disorders were discovered and new techniques for identifying the changes were developed, the World Health Organization (WHO) established a new classification system based on this new information.
The WHO classification is based on multiple parameters: cell staging, morphology and cytochemistry are part of the initial diagnosis; chromosomal changes through karyotype analysis, molecular genetic changes, and immunophenotyping of cell surface markers are then used to more specifically and accurately classify them.
Initial diagnosis also includes relevant clinical data such as medical history, possible toxic exposures, and sometimes physical exam including imaging studies.
