The Impact of Exogenous Estrogen Exposure on the Characteristics and Outcome of Estrogen Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Early-Stage Breast Cancer

Introduction: The impact of exogenous estrogen exposure on breast cancer characteristics and outcomes is not well described. We aimed to investigate the effect of prior treatment with oral contraceptives (OCT), hormone replacement therapy (HRT), and fertility treatments on early-stage, estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer. Methods: This is a single-center retrospective cohort study comprising all women with ER-positive, HER2-negative, early breast cancer whose tumors were sent to Oncotype DX analysis between 2005 and 2012. Data on prior exposures to OCT, HRT, and fertility treatments were collected. The impact of these exposures on prespecified histopathological features was assessed including tumor size, nodal status, intensity of the hormonal receptors, grade, Oncotype recurrence score, Ki67, and lymphovascular and perineural invasion. The impact of these exposures on disease-free survival (DFS) and overall survival (OS) was also evaluated. Results: A total of 620 women were included, of which 19% had prior exposure to OCT, 30% to HRT, and 11% to fertility treatments. OCT use was associated with smaller (<= 1 cm) tumors (p = 0.023) and were less likely to have grade 3 disease (p = 0.049). No other associations were found between exogenous estrogen exposure and tumor characteristics. Median follow-up was 10.4 years. Ten-year DFS was 85.7%, and it was not influenced by exogenous exposure. Ten-year OS was 90.2%, and OCT was associated with improved OS in univariate analysis (HR = 0.31, 95% CI: 0.11-0.85), but this difference did not remain significant in multivariate analysis (p = 0.275). Conclusion: The impact of exogenous estrogen exposure on ER-positive, HER2-negative early breast cancer characteristics is limited. In the long term, none of the evaluated exposures had negative effect on DFS and OS.