Thrombotic Complications and Risk of Myeloid Transformation in 164 Elderly Patients with Essential Thrombocythemia.
Authors: Peterson Erica , Zypchen Leslie , Nitta Janet , Berkowitz Jonathan , Foltz Lynda M 
Published: October 2019

Abstract
Abstract 2916
Poster Board II-892

Introduction:
Essential thrombocythemia (ET) is a myeloproliferative neoplasm associated with increased risk of both venous and arterial thrombosis, hemorrhage and transformation to other myeloid disorders such as myelofibrosis (MF), myelodysplastic syndrome (MDS), and acute myeloid leukemia (AML). Although age greater than 60 years has been shown to be an independent risk factor for thrombosis, data regarding disease outcome and optimal therapy in the very elderly diagnosed with ET is limited. Our aim was to assess rates of thrombo-hemorrhagic complications and transformation in very elderly patients with ET at two tertiary care centers in Vancouver, British Columbia.

Patients and methods:
A retrospective chart review was conducted of all patients diagnosed with ET at age 60 years or older from 1982 to 2008. Data collected included baseline patient characteristics, arterial and venous thrombosis at diagnosis, cardiac risk factors, antiplatelet and cytoreductive therapy throughout the course of the disease, and thrombo-hemorrhagic complications or transformation to AML, MDS or MF during the follow-up period. The patients were separated into three age groups: 60 to 69 years, 70 to 79 years, and 80+ years. Chi-squared tests were used to compare the age groups in terms of baseline characteristics, treatment, thrombotic and hemorrhagic complications, and myeloid transformation. Kaplan-Meier curves for thrombosis and transformation-free survival were generated to follow rates of thrombosis and transformation over time.

Results:
We identified 164 patients diagnosed with ET at age 60 years or older, of which 68 were 60-69 years, 66 were 70-79 years and 30 patients were 80+ years. The median duration of follow-up was 2576 days for the 60-69 group, 1903 days for the 70-79 group, and 453 days for the 80+ group. The three groups were similar in baseline characteristics, including cardiac risk factors, baseline levels of haemoglobin, white blood cells and platelets, as well as the rates of thrombotic or hemorrhagic events at diagnosis. Treatment including the use of ASA (91% 60-69y, 80.3% 70-79y and 75.9% 80+y, p=0.10) and hydroxyurea therapy (67.2% 60-69y, 80.3% 70-79y and 73.3% 80+y, p=0.23) was comparable amongst the three age groups. The number of patients developing thrombotic events during follow up (30.9% 60-69y, 16.7% 70-79y and 13.3% 80+y, p=0.063) and the risk of thrombosis over time (Figure 1A) was similar across the three age groups (p=0.68). The number of patients with myeloid transformation during follow up was greater in the 60-69 age group (25% 60-69y, 9.1% 70-79y and 6.7% 80+y, p=0.013), but the risk of transformation over time was not significantly different (p=0.29) (Figure 1B).

Conclusions:
Age over 60 years has previously been shown to be a risk factor for thrombosis in patients with ET. The current study found no differences in the rates of thrombotic complications, nor myeloid transformation amongst three subgroups of elderly patients with ET. We also note that physicians' treatment approach does not seem to differ amongst these elderly subgroups. Although our data is limited by a small number of very elderly patients, we conclude that the disease course is not different amongst various age groups of elderly patients with ET. With currently available information, there is no reason to consider the disease differently in such patients.

Disclosures:
No relevant conflicts of interest to declare.