Seasonal trends in the self-detection of breast cancer: indications from the Cancer and Steroid Hormone (CASH) study.

Of 2895 women who self-detected an incident breast cancer that required surgery, peaks in month of detection occurred in spring and late autumn (p = 0.012). For the subset of cases for whom receptor status was available, there was a highly significant seasonal variation in detection only for those with ER-negative tumors. Further investigations into seasonality and breast cancer detection may be warranted.