Preferential prescribing of tibolone and combined estrogen plus progestogen therapy in postmenopausal women

In Brief Objective: To verify whether tibolone is preferentially prescribed to women at an increased risk for endometrial and breast cancer compared with women who were prescribed combined estrogen + progestogen therapies, including sequential conjugated equine estrogens/norgestrel, sequential conjugated equine estrogens/medroxyprogesterone acetate, continuous conjugated equine estrogens/medroxyprogesterone acetate, or continuous 17β-estradiol/norethisterone acetate. Design: This was a descriptive study using the General Practice Research Database, a UK primary care database. A total of 16,746 women who, between July 1, 1999, and June 30, 2001, were prescribed either tibolone or one of the estrogen + progestogen regimens listed above were included. The main outcome measures were risk factors associated with endometrial cancer and breast cancer. Results: The clinical background of women who were prescribed tibolone differed from that of women who were prescribed combination products. More frequently than expected, women who were most recently prescribed tibolone had a history of chronic breast disease, a personal history of breast cancer, or a history of (long-term) estrogen-only therapy. Furthermore, medical records of this group of women showed more frequent reports of hypertension and previous uterine procedures. Conclusion: This study confirms previous findings that in the United Kingdom, general practitioners seem to prescribe tibolone preferentially to women with increased risks of breast and endometrial cancer as compared with women who are prescribed estrogen + progestogen products. The findings of this study support the previous observation that tibolone is preferentially prescribed to women with an increased risk for breast and endometrial cancer compared to women being prescribed EPT products in the United Kingdom. The different background risk could introduce a bias in observational studies if adjustment for the different baseline risk is incomplete or not possible.