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 WHO Classification of MDS in Adults:
Refractory Cytopenia with Unilineage Dysplasia (RCUD)
Refractory anaemia 9980/3
Refractory neutropenia 9991/3
Refractory thrombocytopenia 9992/3
Refractory anaemia with ring sideroblasts (RARS) 9982/3
Refractory cytopenias with multilineage dysplasia +/- ring sideroblasts (RCMD) 9985/3
Refractory anaemia with excess blasts (RAEB) 9983/3. RAEB is split in to two groups; RAEB-1 with 5-9% blasts and RAEB-2 with 10-19% blasts.
Myelodysplastic syndrome with isolated del(5q) 9986/3
Myelodysplastic syndrome unclassifiable 9989/3
The WHO Classification of Myelodysplastic/Myeloproliferative Neoplasms in Adults:
Chronic Myelomonocytic anaemia 9945/3
Atypical chronic myeloid leukaemia, BCR-ABL negative 9876/3
Myelodysplastic/Myeloproliferative neoplasms, unclassifiable 9975/3
Refractory anaemia with ring sideroblasts associated with marked thrombocytosis 9982/3. This is a provisional entity, as the WHO group felt there was insufficient evidence to recognize this as a distinct entity at the time of writing.
Each distinct disease entity is given an International Classification of Diseases ICD-0 code. These codes are used worldwide to collect data on morbidity & mortality statistics, and allow automated treatment decisions.
Some extra notes:
Dysplasia must be in ≥10% cells within a cell lineage.
In RARS, ≥15% of erythroid precursors are ring sideroblasts
Patients with RCUD may have unicytopenia or bicytopenia. If they have pancytopenia, they should be classified as MDS-U.
If the blast count is 20% or greater, then the diagnosis is Acute Myeloid Leukaemia.
If Auer Rods are found in the blasts, and myeloblasts in the blood are <5% and <10% in the marrow, then the diagnosis is ‘upgraded’ to RAEB-2.