Estrogen-based hormone treatment (EBHT), in the form of either oral contraceptives or hormone replacement therapy, is generally felt to be associated with an increased risk of thrombosis in women with essential thrombocythemia (ET). However, there is insufficient evidence to support or refute such a concern.


Data was abstracted from medical records of a consecutive cohort of women with ET seen at the Mayo Clinic. Thrombotic risk was determined by the occurrence of a major thrombotic event namely myocardial infarction, angina, cerebrovascular accident, transient ischemic attack, peripheral arterial thrombosis, pulmonary embolism, or deep venous thrombosis at or after diagnosis of ET.


i. Information regarding EBHT at or after the diagnosis of ET

The study cohort included 307 women with ET (median age, 55 years; range 16–88) with a median follow-up of 133 months from diagnosis (range, 0.2–397). EBHT at or after diagnosis was documented in 93 women (30%); 59 patients were on EBHT at time of diagnosis and treatment was initiated after diagnosis in 34 patients. Among the 59 patients who were receiving EBHT at the time of diagnosis, treatment was discontinued within one month of their ET diagnosis in 17 patients but continued in the other 42 patients for a median of 48 months (range, 2–168). In the 34 patients with EBHT that was initiated after the diagnosis of ET, median treatment period was 44 months (range, 1–144).

ii. Correlation between EBHT and thrombosis at diagnosis

At diagnosis, major thrombosis was documented in a total of 74 patients (24%) that included 11 of the 59 patients (19%) on EBHT and 63 of 248 patients (25%) that were not receiving such therapy at the time of diagnosis (p=0.28).

iii. Correlation between EBHT and thrombosis after diagnosis

A total of 95 patients (31%) experienced a subsequent (i.e. post-diagnosis) thrombotic episode during the study period. These occurred in 65 of 214 patients (30%) that were not exposed to EBHT at or after diagnosis, 5 of 17 patients (29%) in whom EBHT was discontinued with the diagnosis of ET, 13 of 42 patients (31%) in whom EBHT was continued despite the diagnosis of ET, and 12 of 34 patients (35%) in whom EBHT was started after the diagnosis of ET (p=0.95). Furthermore, duration of EBHT, using a cutoff value of 1 year, did not significantly affect the incidence of thrombotic events (p=0.67).

The different comparative groups were similar in age distribution as well as frequency of other cardiovascular risk factors including smoking, diabetes mellitus, hypertension, and hyperlipidemia.


The current study addresses the important issue of safety pertaining to the use of estrogen-based hormones in women with ET and did not reveal a significant alteration of thrombosis risk as a result of hormone therapy.

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