Seasonality and breast cancer.

We have analysed the data of biopsy, tumour size, size, side and axillary lymph node status in a group of 866 patients presenting with breast cancer in Southampton from September 1975 to August 1981 and a group of 1424 women presenting with benign disease in the same period. The whole group showed a seasonal variation, with a peak presentation in June. The pre-menopausal age group account for almost all of this seasonality. The cause of the variation is not established and requires further investigation. The control group of benign breast disease cases did not show a seasonal variation.