A new study has reported that premenopausal women who have their ovaries removed as part of treatment for breast cancer are more likely to survive if the surgery takes place during the second half of their menstrual cycles (between ovulation and the first day of the next menstrual cycle). Adjuvant surgical oophorectomy (removal of the ovaries) is a useful and cost effective treatment for premenopausal women with early stage hormone receptor positive breast cancer. Previous reports have suggested a survival benefit for patients whose surgery was performed in the luteal phase (between ovulation and menstruation) of the menstrual cycle as opposed to the follicular phase (first part of the cycle, which starts with the first day of menstruation).

The study included women recruited to a clinical trial which began in 1993. The trial was designed to investigate treatment with adjuvant surgical oophorectomy plus five years of tamoxifen. The authors recorded day 1 of the patients' last menstrual cycle before surgery (as reported by the women) and estimated whether surgery occurred during the luteal or follicular phase of their menstrual cycles.

Women who had their ovaries removed during the luteal phase were twice as likely to survive (overall survival) as those who had surgery during the follicular phase. Disease-free survival also tended to be enhanced among women who had surgery during the luteal phase of the menstrual cycle, but this result was not statistically significant. The effect of timing of surgery on disease-free survival diminished after six years. The authors conclude that adjuvant surgical oophorectomy during the luteal phase of the menstrual cycle resulted in a reduced risk of recurrence compared to removal of the ovaries in the follicular phase during the first 5.5 years of follow-up among the study population. The practical and biological implications of these findings deserve rigorous evaluation in clinical trials, according to the authors.