Timing of Adjuvant Surgical Oophorectomy in the Menstrual Cycle and Disease-Free and Overall Survival in Premenopausal Women With Operable Breast Cancer

Background: For women with hormone receptor-positive, operable breast cancer, surgical oophorectomy plus tamoxifen is an effective adjuvant therapy. We conducted a phase III randomized clinical trial to test the hypothesis that oophorectomy surgery performed during the luteal phase of the menstrual cycle was associated with better outcomes. Methods: Seven hundred forty premenopausal women entered a clinical trial in which those women estimated not to be in the luteal phase of their menstrual cycle for the next one to six days (n = 509) were randomly assigned to receive treatment with surgical oophorectomy either delayed to be during a five-day window in the history-estimated midluteal phase of the menstrual cycles, or in the next one to six days. Women who were estimated to be in the luteal phase of the menstrual cycle for the next one to six days (n = 231) were excluded from random assignment and received immediate surgical treatments. All patients began tamoxifen within 6 days of surgery and continued this for 5 years. Kaplan-Meier methods, the log-rank test, and multivariable Cox regression models were used to assess differences in five-year disease-free survival (DFS) between the groups. All statistical tests were two-sided. Results: The randomized midluteal phase surgery group had a five-year DFS of 64%, compared with 71% for the immediate surgery random assignment group (hazard ratio [HR] = 1.24, 95% confidence interval [CI] = 0.91 to 1.68, P =.18). Multivariable Cox regression models, which included important prognostic variables, gave similar results (aHR = 1.28, 95% CI = 0.94 to 1.76, P =.12). For overall survival, the univariate hazard ratio was 1.33 (95% CI = 0.94 to 1.89, P =.11) and the multivariable aHR was 1.43 (95% CI = 1.00 to 2.06, P =.05). Better DFS for follicular phase surgery, which was unanticipated, proved consistent across multiple exploratory analyses. Conclusions: The hypothesized benefit of adjuvant luteal phase oophorectomy was not shown in this large trial.