Đến năm 1960, ET nói chung được chấp nhận như một thực thể khác biệt clinicopathologic (Gunz 1960) và các tiêu chuẩn chẩn đoán nghiêm ngặt đã được thành lập sau này trong những năm 1970 bởi nhóm nghiên cứu vera đa hồng cầu | Disease Classification 323 1951 . Initial descriptions of the latter MPD antedated that of ET CML was first described in 1845 Virchow 1845 PV in 1892 Vaquez 1892 MMM in 1879 Heuck 1879 and erythroleukemia in 1917 Di Guglielmo 1917 . By 1960 ET was generally accepted as a distinct clinico-pathologic entity Gunz 1960 and strict diagnostic criteria were established later in the 1970s by the polycythemia vera study group PVSG Murphy et al. 1986 . In 1981 Fialkow and colleagues utilized G-6-PD isoenzyme analysis to demonstrate that ET represented a stem-cell-derived clonal myeloproliferation Fialkow et al. 1981 . In 2005 an activating JAK2 mutation Jak2V617F was demonstrated in MPD James et al. 2005 a and it was shown to be present in approximately half of the patients with ET Baxter et al. 2005 Kralovics et al. 2005 Levine et al. 2005 . However the pathogenetic relevance of the latter observation remains to be defined Goldman 2005 . Disease Classification At present classification of myeloid disorders including ET is in general based on a constellation of clinical bone marrow histological cytochemical chromosomal and immunophenotypic features Jaffe et al. 2001 . Accordingly the World Health Organization WHO system for classification of myeloid neoplasms classifies chronic myeloid disorders into four separate categories MPD MDS MPD MDS and systemic mastocytosis SM Var-diman et al. 2002 . The WHO MPD category includes the four classic . Dameshek s MPD CML ET PV MMM and in addition chronic neutrophilic leukemia CNL chronic eosinophilic leukemia CEL hypereosi-nophilic syndrome HES and unclassified MPD UMPD . The WHO MDS MPD category includes chronic myelomonocytic leukemia CMML juvenile myelomonocytic leukemia JMML and atypical CML. However most chronic myeloid disorders including MDS classic MPD and atypical MPD have now been shown to represent a clonal stem cell process Adamson et al. 1976 Bain 2003 Barr and Fialkow 1973 Fialkow et al. 1967 1977 1978 a 1981
