Why do we need a classification?
It allows us to have a common language. A classification standardises the features by which a disease entity is diagnosed, allows us to study specific diseases and also to instigate appropriate treatments.
What is the WHO Classification of Tumours of the Haemopoietic and Lymphoid Tissues?
This is a joint project between the European Association for Haematopathology and the Society for Haematopathology. It is a worldwide consensus for the classification of haematological malignancies. The latest update is the 4th Edition and was published in 2008. It incorporates morphology, immunophenotypic and genetics features.
THE UPDATED WHO CLASSIFICATION OF HEMATOLOGICAL MALIGNANCIES
The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia
You can read the review here