Timing of breast cancer surgery in relation to the menstrual cycle--the rise and fall of a hypothesis.

It has been claimed that the timing of surgery in relation to the menstrual cycle can significantly influence the prognosis among premenopausal women with primary breast cancer. The literature on the subject is reviewed. The results are heterogeneous, and the quality of the studies is in general low. Many studies suffer from statistical problems concerning small sample sizes and sub-group analyses. In all, the scientific basis for the hypothesis seems weak.