The impact of endogenous estrogen exposures on the characteristics and outcomes of estrogen receptor positive, early breast cancer

Background: Menstrual and parity history might impact the risk for breast cancer. Data on the impact of these factors on other tumor characteristics are limited. Methods: A single center retrospective cohort study comprising all women with estrogen receptor (ER) positive, human epidermal growth factor receptor 2 (HER2) negative, early breast cancer whose tumors were sent to OncotypeDX analysis. The prespecified subgroups were investigated: age of menarche (< 12 vs. ≥ 12 years), number of deliveries (0 vs. ≥ 1 childbirth and ≥ 5 childbirth vs. other), age of first delivery (≥ 30 years vs. younger age) and postmenopausal compared to premenopausal. The impact of age of menopause was also assessed categorically, using early (< 45 years) and late age of menopause (> 55 years). Differences in tumor characteristics were evaluated using T-test or Mann Whitney for continuous variables or Fisher’s exact test for categorical variables. Outcomes were assessed by Kaplan–Meier survival analysis, with the log-rank test. Results: A total of 620 women were included. After median follow-up of 10.4 years, early menopause was associated with significantly worse disease-free survival (HR = 2.26, p = 0.004) and overall-survival (HR = 2.60, p = 0.004), and multiparity was associated with significant worse disease-free survival (HR = 2.16, p = 0.026). These differences remain significant in multivariate analyses. Post-menopausal women were more likely to have stronger ER intensity (p = 0.002) but progesterone receptor (PR) positivity was less frequent (p = 0.009(. Early age of menarche was associated with PR positivity (p = 0.039). No other associations were found between the evaluated subgroups and tumor characteristics. Conclusions: The impact of endogenous estrogen exposure had little effect on breast cancer characteristics of early stage, luminal disease. Early menopause and multiparity were associated with worse outcome.