Essential thrombocythemia (ET) is a Philadelphia chromosome-negative Myeloproliferative Disease characterized by a relatively indolent clinical course, a predisposition to thrombotic and bleeding events, and a delayed occurrence of disease transformation into myelofibrosis (MF) or acute myelogenous leukemia (AML) in selected patients (pts). Current therapy for ET has not been shown to affect in a positive way either survival or risk of disease transformation.

We retrospectively assessed 158 pts with ET seen at our institution between November 1983 and February 2006, and evaluated their long-term outcome, risk of disease complications and transformation, and prognostic factors for both survival and disease complications. Median age was 51 years (range, 17–83), 59% were females. The median time from diagnosis to MD Anderson visit was 5 years (range 0–21) and from MD Anderson visit median follow up was 1.5 years (range 0–19). Fifty-two % of pts had received therapy before MD Anderson visit. At presentation 53% of the pts were symptomatic, including fatigue in 32%, weight loss in 8%, headache in 7%, and night sweats in 5%; splenomegaly was present in 18 pts (11%); median hemoglobin was 13.3 g/dL (range 7.1–16.6), white blood cell count 9.4 × 109/L (range 1.9–21.9), and platelets 909 × 109/L (range, 153–1000 × 109/L); karyotype was diploid in 129 of 139 evaluable pts (93%).

During the follow up 34 pts (22%) have never received any cytoreductive therapy, while 66 pts (42%) received more than one therapy. Therapy included hydroxyurea in 71 (45%), anagrelide in 47 (30%), and interferon/pegylated interferon in 67 pts (42%). Thrombotic and bleeding events occurred in, respectively, 33 (21%; 22 arterial and 11 venous thrombosis) and 29 (18%) pts. Transformation to MF occurred in 7 (4%) pts after a median of 73 months (range 5–159). At tranformation the karyotype was diploid in all but one pt (+1, der (1;17)(q10;q10), +8). Presently 135 pts (85%) are alive. The 5-year and 10-year overall survivals from MD Anderson visit were, respectively, 88.5% and 77.3%. The median survival has not been reached. The multivariate analysis of patients’ characteristics at presentation to and since MD Anderson visit identified interferon therapy as favorable predictive factor for survival (unlike other therapies). In contrast, this therapy constitutes an independent risk for a thrombotic event. No predictive factor for transformation has been identified.

We conclude that ET is a good prognosis disease with a low rate of transformation into more aggressive disease, and that interferon therapy may improve the outcome. Patients were referred to MD Anderson at different time in the natural history of their disease, and the evaluation of probable impact of interferon therapy on patients’ survival in ET should be verified in newly diagnosed patients.

Disclosure: No relevant conflicts of interest to declare.

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