Reply to F. Tomao et al

We thank Tomao et al1 for their correspondence in reference to our article,2 in particular, for suggesting biases that may have arisen because of factors related to a lower risk of endometrial cancer among patients using bisphosphonates. Common hormonal medications that have been shown to reduce endometrial cancer risk,3 specifically oral contraceptives and progestin, were, in fact, included in our statis-ticalmodels. Use of gonadotropin-releasing hormone agonists for the treatment of endometriosis or other benign gynecologic diseases was not yet common, particularly among postmenopausal women, when the Women’s Health Initiative (WHI) investigators began recruiting in 1993.4 Therefore, we do not believe our inability to adjust for their use distorted our results. Statins have been associated with a reduced riskofendometrial cancer inprevious reports,5,6 andananalysisof this association in the WHI is forthcoming.7 During the early years of follow-up, however, statins were not as frequently prescribed as they are today, and previousWHI analyses have not shown statin use to be related to the risk of other hormonal cancers8,9 or indications for bisphosphonate use.10 As we noted, our study had an observational design, and therefore, a causal relationship between bisphosphonate use and endometrial cancer remains to be established