Hormone levels change during the menstrual cycle, leading to changes in the way the breasts both look and feel. It is well known that female hormones have a number of effects on the development and growth of many breast cancers.

In 1989 a report suggested that if women had their surgery to remove a breast cancer at around the time of their periods they had a better chance of a cure than if the operation was done at other times during their menstrual cycle.

Although this was a very interesting result it was based on a very small number of patients, with only 41 women in the study. The findings of such a small study could not really be relied on. Since then many other studies have been done to try and see whether the timing of surgery during the menstrual cycle really does make a difference.

The menstrual cycle can be divided into two parts. The first is known as the proliferative, or follicular, phase. This lasts for about two weeks from the start of a period. During this time the womb is prepared for ovulation (the release of the female egg from the ovary). Ovulation occurs on about the fourteenth or fifteenth day of the cycle. After ovulation, assuming there isn't a pregnancy, the cycle moves into the luteal phase, which lasts anywhere from fourteen to twenty eight days, and then the next period starts.

A lot of the studies that have looked at the timing of breast cancer surgery during the menstrual cycle have been carried out with small numbers of patients and have given differing results. Some studies have suggested there may be a benefit for operating in the luteal phase while others haven't found any difference.

Because research studies have not given a clear answer to this question this issue is still controversial.

Overall, at the present time most hospitals do not routinely take into account the phase of the menstrual cycle when planning surgery for breast cancer. This is because it is generally believed that it makes no difference to the chance of curing the cancer.