World Health Organization Classification of tumors of hematopoietic and lymphoid tissues, 4th edition, 2008 - major changes from the 3rd edition, 2001

The World Health Organization (WHO) classification of Tumors of Hematopoietic and Lymphoid Tissues (4th edition, 2008) represents an update of the 3rd edition, 2001.2 A summary of these changes in myeloproliferative disorders, myelodisplastic syndrome, acute myeloid leukemias, B and T precursor cell neoplasms, and mature B, T and NK cell neoplasms is presented below. Understanding the molecular genetic changes and the results achieved with innovative therapeutic approaches in these groups of diseases require continuous reassessment of its classification, justifying the major changes discussed here 1,3-5 .