Timing of breast cancer surgery in relation to the menstrual cycle: an update of developments.

It is well-established that hormones have multiple effects on breast cancer. Some, but not all studies indicate that the phase of the menstrual cycle (and hence hormonal status) at the time of breast surgery may influence survival. In this paper we review the literature in this area, explore how it is possible that such an association may occur, and note that randomised studies which unambiguously determined the phase of the cycle at the time of the operation are lacking. We go on to describe an ongoing self-randomised trial designed to address this problem and present preliminary results which show that only about 75% of the women ovulated during the cycle in which the operation took place, and that the established prognostic factor Ki-67 varied with the phase of the cycle in women who ovulated. It is too early to assess the significance of this finding.