The major disease of hematopoietic cells fall into several categories, which include chronic myeloproliferative disease, myelodysplastic syndromes, leukemias, lymphomas, plasma cell neoplasms, and histiocytic and mast cell neoplasms. Hematopathologists from all over the world have agreed on a standard classification system, called the "WHO classification". Leukemias are mainly bone marrow and blood based and can be subclassified as chronic leukemia and acute leukemia. Chronic leukemia is the proliferation of too many mature blood cells, and is called that because it is a chronic process clinically. Examples are chronic myelogenous leukemia and chronic lymphocytic leukemia. Acute leukemia is the proliferation of too many immature blood cells, called myeloblasts, which have lost the ability to become mature cells. This is usually a very aggressive disease if untreated. Fortunately, treatment of both types of leukemia has improved greatly over the past few decades. Lymphomas are diseases that are mainly based in lymph nodes. Hematopathologists have named different lymphomas after the type of lymphocyte that has become malignant. Thus there are B cell lymphomas, T cell lymphomas, and NK cell lymphomas. The hematopathologist uses immunohistochemistry and flow cytometry, techniques using antibodies to specific cell surface antigens, to determine the type of hematopoietic neoplasm in the pathology specimen.