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1308 Part X: Malignant Myeloid Diseases Chapter 85: Essential Thrombocythemia 1309

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Figure 85–2. Morphologic features of essential thrombocythemia. A. Contrast-enhanced abdominal computed tomography (CT) scan showing
features of established hepatic vein thrombosis in a 53-year-old female, including hypertrophy of the caudate lobe (arrow) with atrophy of the
remaining liver and surrounding ascites; the spleen is of normal size. Hematoxylin and eosin (H&E)-stained marrow trephine biopsy showing normal
cellularity and increased megakaryocytes with occasional hyperlobulated forms (inset). Although the patient was JAK2 V617F -positive, other investiga-
tions performed at this time, including blood count, red cell mass and cytogenetic analysis, were normal. B. Marrow aspirate from a JAK2 V617F -positive
essential thrombocythemia (ET) patient showing large, hyperlobulated megakaryocytes (slide stained with Wright-Giemsa). C. Marrow trephine
biopsy samples from patients with ET (slide stained with H&E).

in vitro coagulation studies, including abnormal platelet aggregation or disease duration is a major predictor of progressive disease, with rates
loss of large von Willebrand factor multimers; however, the relationship of myelofibrosis in the first decade after diagnosis of 3 to 10 percent ris-
of these findings to episodes of clinical bleeding is unclear. In a pro- ing to 6 to 30 percent in the second decade. 34,40 The presence of marrow
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spective study, rates of major hemorrhage were increased in patients fibrosis at diagnosis also appears to presage progression to myelofibro-
with increased marrow fibrosis at diagnosis and in those with an sis, although the predictive value of other histologic features of early
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increased platelet or leucocyte count during followup. 35 stage PMF, such as megakaryocyte dysplasia, remains controversial.
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Mutations in JAK2, 42,43 MPL, 17,18 or CALR 44,45 appear to lack prognos-
tic significance. A prospective study of high-risk ET patients indicated
MYELOFIBROTIC TRANSFORMATION increased progression to myelofibrosis with anagrelide therapy, with
Evolution to myelofibrosis is seen in a proportion of ET patients, a 5-year cumulative incidence of 7 percent for anagrelide plus aspirin
although the reported prevalence varies widely, reflecting differences versus 2 percent for hydroxyurea plus aspirin-treated patients. The
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in study design, therapeutic intervention and diagnostic criteria for clinical consequences of post-ET myelofibrosis are similar to de novo
post-ET myelofibrosis (Chap. 86). Retrospective studies suggest that myelofibrosis, and the conditions are managed in the same way.

Kaushansky_chapter 85_p1307-1318.indd 1309 9/21/15 11:08 AM