Conjugated estrogens/bazedoxifene use tied to higher rates of endometrial cancer, hyperplasia

In the first years of use, conjugated estrogens/bazedoxifene (CE/BZA) appears to be associated with slightly higher rates of endometrial cancer and endometrial hyperplasia compared with estrogen/progestin (EP) combination hormone therapy, according to a study.

For the study, researchers used five US healthcare claims databases representing more than 92 million women. New users of CE/BZA or EP were identified and matched using propensity score (PS). Claims-based algorithms facilitated ascertainment of the incidence of endometrial cancer, endometrial hyperplasia, breast cancer, and eight additional cancer and cardiovascular outcomes.

A total of 10,596 CE/BZA and 33,818 PS-matched EP new users comprised the study population. Treatment duration was slightly longer in the CE/BZA group in most databases. The average follow-up time for cancer outcomes was about 22 months, while the average follow-up time for endometrial hyperplasia and cardiovascular outcomes was between 10 and 11 months.

Compared with EP users, CE/BZA users had slightly higher rates of endometrial cancer and endometrial hyperplasia (1.6 and 0.4 additional cases per 10,000 person-years). However, precision was limited due to the small numbers of cases (endometrial cancer: rate ratio [RR], 1.50, 95 percent confidence interval [CI], 0.79–2.88; endometrial hyperplasia: RR, 1.69, 95 percent CI, 0.51–5.61).

Meanwhile, the incidence of breast cancer incidence was lower among CE/BZA than EP users (9.1 fewer cases per 10,000 person-years; RR, 0.79, 95 percent CI, 0.58–1.05). For other outcomes, the incidence rates were slightly higher among CE/BZA users, but the confidence intervals were wide.