No differences found for mortality
Of the 8,461 women in the study, 40% (3,370) died during an estimated median follow-up of 15.2 years. Of those, 497 had received VET, 47 MHT, and 2,826 neither. Compared with the never-users of estrogen therapy, the adjusted HR for overall survival in VET users was 0.78 (95% CI, 0.71-0.87). The analysis stratified by adjuvant endocrine therapy didn’t show an increase in VET users by use of aromatase inhibitors (aHR, 0.94, 95% CI, 0.70-1.26). The same was found for women prescribed MHT, compared with never-users (aHR, 0.94; 95% CI, 0.70-1.26).
Never-users of VET or MHT had an absolute 10-year overall survival of 73.8% versus 79.5% and 80.5% among the women who used VET or MHT, respectively.
Asked to comment, Nanette Santoro, MD, professor and E. Stewart Taylor Chair of Obstetrics & Gynecology at the University of Colorado at Denver, Aurora, said in an interview: “It is important to look at this issue. These findings raise but don’t answer the question that vaginal estradiol may not be as safe as we hope it is for women with breast cancer using an aromatase inhibitor.”
However, she also pointed out that “the overall increase in risk is not enormous; mortality risk was not increased. Women need to consider that there may be some risk associated with this option in their decision making about taking it. Having a satisfying sex life is also important for many women! It is really compassionate use for quality of life, so there is always that unknown element of risk in the discussion. That unknown risk has to be balanced against the benefit that the estrogen provides.”
And, Dr. Santoro also noted that the use of prescription data poses limitations. “It cannot tell us what was going on in the minds of the patient and the prescriber. There may be differences in the prescriber’s impression of the patient’s risk of recurrence that influenced the decision to provide a prescription. ... Women using AIs [aromatase inhibitors] often get pretty severe vaginal dryness symptoms and may need more estrogen to be comfortable with intercourse, but we really cannot tell this from what is in this paper.”
Indeed, Dr. Cold said: “We admit it’s not a randomized study, but we’ve done what was possible to take [confounding] factors into account, including age, tumor size, nodal status, histology, and comorbidities.”
He suggested that a potential therapeutic approach to reducing the recurrence risk might be to switch VET-treated women to tamoxifen after 2-3 years of aromatase inhibitors.
This work was supported by Breast Friends, a part of the Danish Cancer Society. Dr. Cold received support from Breast Friends for the current study. Some of the other coauthors have pharmaceutical company disclosures. Dr. Santoro is a member of the scientific advisory boards for Astellas, Menogenix, Que Oncology, and Amazon Ember, and is a consultant for Ansh Labs.