CONFERENCE UPDATE (ASCO 2025)

SEER-MHOS analysis supports the use of local estrogen therapy in breast cancer patients

Anti-hormonal therapies such as tamoxifen and aromatase inhibitors are the cornerstone of treatment for hormone receptor-positive (HR+) breast cancer.1 However, these treatments can result in genitourinary syndrome of menopause (GSM), characterized by vaginal dryness, irritation, and discomfort, which may be alleviated by vaginal estrogen therapy.1 However, concerns about its safety in breast cancer patients may have resulted in the potentially undue avoidance of hormone-based treatments, depriving patients of needed symptomatic relief.1 During the 2025 ASCO Annual Meeting, Dr. Olivia Mitchel presented the findings from a retrospective cohort study exploring the association between vaginal estrogen use and survival outcomes in breast cancer patients, using data from the Surveillance, Epidemiology and End Results Medicare Health Outcomes Survey (SEER-MHOS) database.1

The retrospective cohort study included data from 18,620 female breast cancer patients aged ≥65 years diagnosed between 2007 and 2017  in the SEER-MHOS registry.1 Among them, 800 patients received vaginal estrogen therapy, while 17,820 did not.1 Outcomes assessed included overall mortality and breast cancer-specific mortality.1 Multivariate regression models were applied to adjust for age, race, cancer stage, treatment, and year of diagnosis.1 Subgroup analyses focused on HR+ breast cancer patients.1

Vaginal estrogen use was associated with significantly improved survival outcomes.1 Patients using vaginal estrogen demonstrated a significant reduction in overall mortality compared to non-users (HR=0.56; p<0.0001).1 This pattern persisted in HR+ breast cancer patients (HR=0.62; p=0.0007).1 Similarly, vaginal estrogen use was linked to a significant reduction in breast cancer-specific mortality (HR=0.53; p=0.014).1 Although a decrease in breast-cancer-specific mortality was also observed in HR+ patients, it did not reach statistical significance (HR=0.62; p=0.08).1 Longer duration of vaginal estrogen use was also found to be associated with a significant reduction in overall mortality.1 Patients using it for more than seven years showed a substantial decrease in mortality compared to those with shorter use (HR=0.01; p<0.0001).1

In conclusion, the findings add to a growing body of evidence showing that vaginal estrogen use does not increase the risk of overall and breast cancer-specific mortality, suggesting that local hormone therapy may be safer than previously assumed for managing GSM in patients receiving anti-hormonal treatment.1 This was consistent with findings from Dr. Mitchel’s latest round of analysis, which adjusted for a quality-of-life index, providing further support to this conclusion.1 These results challenge the long-standing concerns regarding vaginal estrogen therapy in breast cancer patients and support its judicious use for GSM management.1

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Ribociclib plus fulvestratnt has the longest mOS OF over 67 months in postmenopausal breast cancer patients

Cancer is a leading cause of death globally, claiming almost 10 million deaths in 2020.1 Breast cancer is one of the most common cancers in women, with nearly 2.3 million new breast cancer diagnoses in 2020 worldwide.1 Gene-expression profiling has identified distinct subtypes of cancer, among which there are subpopulations expressing specific markers.2 According to the National Institutes of Health (NIH), hormone receptor-positive/human epidermal growth factor 2-negative (HR+/HER2-) is the most prevalent breast cancer.3 Cyclin-dependent kinase 4 and 6 (CDK4/6) are good drug targets for cancer, owing to their role in cell cycle progression.4 Ribociclib is one of the 3 inhibitors of CDK4/6 approved in combination with fulvestrant for treating HR+/HER2- advanced breast cancers in adults, based on a series of phase 3 clinical trials called MONALEESA, which tested ribociclib along with different drug partners in HR+/HER2- cancer patients.4-7 The MONALEESA-2 study showed that progression-free survival (PFS) was significantly longer with first-line ribociclib + letrozole than with placebo + letrozole.7 The MONALEESA-7 trial also showed significantly longer median overall survival (mOS) in ribociclib in combination with the endocrine therapy (ET) vs. the placebo arm in postmenopausal HR+/HER2- cancer patients.6 Similarly, the primary MONALEESA-3 trial and its subsequent analysis Demonstrated that ribociclib + fulvestrant had significant OS benefit as compared with placebo in HR+/HER2- patients advanced breast cancer patients.5,6 In a recently held European Society of Medical Oncology (ESMO) Breast Cancer Congress, Neven, et al. presented an updated exploratory mOS analysis result with the longest follow-up of the MONALEESA 3 study to date.8

05 Jul 2022