Haematological classification of the chronic myeloid leukaemias.

Chronic myeloid leukaemia (CML) includes five subtypes, and the term should be used in the same way as the term chronic lymphoid leukaemia to refer to a group of related conditions. The subtypes of CML are: 1. Chronic granulocytic leukaemia (CGL) (95% of all CML; 90% are Ph+, BCR+, 5% are Ph-, BCR+); 2. Juvenile CML (extremely rare; Ph-, BCR- in the few so far examined); 3. Chronic neutrophilic leukaemia (CNL) (extremely rare; Ph-, BCR- in the few so far examined); 4. Chronic myelomonocytic leukaemia (CMML). CMML with low or normal leukocyte counts is classified as a myelodysplastic syndrome; CMML with high leukocyte count is both myelodysplastic and myeloproliferative. Ph-, BCR-; 5. Atypical CML (aCML). Intermediate between CGL and CMML but has distinctive features. Ph-, mostly BCR-. Significance of few reported BCR+ uncertain. Markedly worse survival than CGL and probably worse than CMML. Definition needs refining. Types 2, 3, 4 and 5 account for 5% of all CML. CGL, CMML, aCML and CNL can be diagnosed in the great majority of cases from the morphological profile of presentation peripheral blood films, but high-quality Romanowsky staining is essential.