Estrogen-based hormone therapy and thrombosis risk in women with essential thrombocythemia

BACKGROUND. There is currently insufficient evidence to either support or refute an association between estrogen-based hormone treatment (EBHT) and thrombosis risk in essential thrombocythemia (ET). METHODS. A retrospective review of thrombotic events, which occurred both at diagnosis of ET and during subsequent follow-up, was performed in a consecutive cohort of women with WHO-defined ET seen at the Mayo Clinic. Details of EBHT were concomitantly obtained. RESULTS. A total of 305 women were seen during the study period and followed for a median of 133 months. EBHT at diagnosis was documented in 59 women and such therapy was instituted at a variable time after diagnosis in 34 additional patients. At diagnosis, major thrombosis occurred in 73 patients (24%), including I I of 59 (19%) on EBHT and 62 of 246 (25%) not on EBHT (P =.28). Thrombosis after diagnosis occurred in 94 patients (31%), including 64 of 212 (30%) not on EBHT, 5 of 17 (29%) in whom EBHT was discontinued at diagnosis, 13 of 42 (31%) in whom EBHT was continued despite the diagnosis of ET, and 12 of 34 (35%) in whom EBHT was started after diagnosis (P =.95). The overall results were the same when arterial and venous events were analyzed separately. However, EBHT in the form of oral contraceptives (OCP) was associated with an increased risk of venous thrombosis (P =.03). CONCLUSIONS. EBHT is safe in ET outside the setting of OCP use, which might be associated with an increased risk of deep vein thrombosis.