Menstrual Cycle Study

1 June 2009


This American coordinated study evaluated whether the timing of breast cancer surgery during a woman’s menstrual cycle affects her ultimate outcome, that is, the likelihood of recurrence of her breast cancer or death.

Scientific Title

IBCSG 21-99/NCCTG N9431: Menstrual Cycle and surgical treatment of breast cancer.


Controversy regarding a possible link between menstrual cycle phase (follicular or luteal) at the time of surgery for breast cancer, and breast cancer outcome existed over the 1980s-1990s. A majority of past information on the menstrual phase had been obtained from research looking back at charted documentation of a woman’s last menstrual period. This approach lacked the accuracy of the date of the last menstrual cycle.


This large international collaborative study where menstrual phase was determined by the measuring of hormonal levels in blood samples taken within one day of surgery has finally put this issue to rest. Results showed there is no relationship between breast cancer recurrence or overall survival and timing of surgery on the basis of the menstrual cycle phase for premenopausal (still having periods) women with early-stage breast cancer.

Publication:  Menstrual cycle and surgical treatment of breast cancer: findings from the NCCTG N9431 study. Grant CS, Ingle JN, Suman VJ, Dumesic DA, Wickerham DL, Gelber RD, Flynn PJ, Weir LM, Intra M, Jones WO, Perez EA, Hartmann LC.  Journal  Clinical Oncology; 2009; 27(22):3620-3626.