RESEARCH SPOTLIGHT
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In October 2022, the Journal of the National Cancer Institute (JNCI) published findings from a Danish research team led by Cold and colleagues in a paper entitled Systemic or Vaginal Hormone Therapy After Early Breast Cancer: A Danish Observational Cohort Study. In this large, population-based observational study, 8,461 postmenopausal women ages 35-95 years old (median age 61 yo) with early-stage, non-metastatic ER+ breast cancer who were not using any hormone therapy (75%, N=6,371) or who were prescribed vaginal estrogen therapy (VET; 25%, N=1,957) or systemic hormone therapy (MHT; 2%, N=133) after their cancer diagnosis were included in study analyses.
After a median follow-up of 9.8 years, authors found VET users did not have increased risk of cancer recurrence compared to non-users (HR=1.08, 95% CI 0.89-1.32). However, in subgroup analyses, VET users who were taking an aromatase inhibitor (AI) had elevated risk of cancer recurrence compared to non-users (HR=1.39, 95% CI = 1.04-1.85). VET users, including the subgroup of those taking an AI, did not have any increased risk of cancer-related mortality compared to non-users. The authors state this is the first study to report a possible increased risk of breast cancer recurrence in patients on AIs who used a vaginal estrogen. Interpretation of these findings should take into consideration important methodologic limitations including the non-randomized study design and lack of information on route, dose, and frequency of VET use.
Professional Perspectives
The researchers' conclusions of this study have been making waves since publication. Here to offer their own practical perspectives and interpretations of study findings are two of the Scientific Network’s very own experts in the field:
- Dr. Sharon Bober (Dana Farber Cancer Institute): This Danish study looked at longitudinal data from a cohort of postmenopausal women, 1997-2004, examining either vaginal estrogen therapy (VET) or systemic therapy. They evaluated mortality and risk of recurrence associated with use of VET and in subgroup analysis found that there was an increased risk of recurrence, but not mortality, in women who used VET with adjuvant AIs.
However, the issue is that the dose or delivery system of vaginal estrogen is not addressed. The Vagifem (estradiol vaginal tablet) dose was 25 mcg until 2010. After 2010, doses went from 25 mcg to 10 mcg. We currently also have other low dose options like Imvexxy, which is a 4-mcg estradiol tablet. Because this data was from 1997-2004, I think it is likely that the dose of vaginal estrogen women were getting between 1997-2004 was significantly more than we give women now. Moreover, how VET is delivered was also not addressed, and dosing again can vary significantly depending on how topical estrogen is being delivered. I think it is important not to jump to conclusions about vaginal estrogen being contraindicated for women on AIs based on this study alone.
- Dr. Stacy Tessler Lindau (UChicago Medicine): This study from Denmark is an important addition to the limited knowledge base available to effectively counsel post-menopausal women with ER+ breast cancer about treatment options for the very common and distressing problems of vaginal dryness, dyspareunia, and loss of capacity for sexual activity that result from anti-estrogen therapies. As the authors point out, a prospective randomized controlled trial would be the gold standard study and is needed given the high prevalence of (distressing and costly) genitourinary symptoms and loss of sexual activity among women with ER+ breast cancer.
This retrospective (1997-2004), observational study uses a large, unique, and high-quality data source. The focus is post-menopausal Danish women with early-stage ER+ breast cancer who did not receive chemotherapy (so findings may not be pertinent to people with early-stage cancer diagnosed pre-menopause, those with later stage cancer or those who did receive chemotherapy). As the authors acknowledge, the findings may be affected by factors for which the study could not account and so translation of the findings should take this limitation into account. Furthermore, among the group using vaginal estrogen, multiple modalities of vaginal estrogen therapy were documented. In supplementary material, the authors identify Estring (estradiol vaginal ring), Ovestin (estriol cream) and Vagifem (estradiol tablet) as among the vaginal estrogen therapies that women in this study may have used. However, it is important to consider that the analysis does not differentiate between these – in other words, we do not know whether mode (e.g., ring, cream, tablet) or estrogen type (e.g., estradiol, estriol) or dose might have conferred different levels of risk (or even protection) against recurrence. Of note, estriol cream is not FDA-approved for use in the US. The observed association likely reflects, at least in part, the dominant modality used in this population during the study period, but this information is not disclosed in the paper.
In addition, the study does not fully account for estrogen use pre-diagnosis, but another study reports that rates of estrogen use in the general Danish population at that time were nearly 40% among menopausal women. Only women with documented HRT or VET use in the two years before a breast cancer diagnosis were excluded (Figure 1 indicates 1249 excluded for use of VET or MHT before BC, but the methods indicate that only use in the prior two years was examined). Rates of estrogen use in the Danish population are well characterized and may have been higher than a comparable, contemporaneous (1997-2004) U.S. population.
Practically speaking, current practice guidelines in the U.S. already recommend non-hormonal vaginal modalities as first line treatment of vaginal symptoms in ER+ breast cancer patients. This study corroborates those recommendations. It is also important to note that while there is a higher rate of diagnosed recurrence, there is not a higher rate of mortality in the subgroup of ER+ breast cancer patients on AI therapy. This finding could be driven by a higher rate of detection of recurrence in the AI subgroup (e.g., closer vigilance). A more accurate conclusion for this study would be: “For early-stage, post-menopausal, BC patients receiving adjuvant AIs, vaginal estrogen therapy should be used with caution.” This conclusion is consistent with current practice.
Additional Perspectives
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