Seasonal variation in breast cancer detection: correlation with tumour progesterone receptor status.

A significant circannual variation of the month in which patients detect the first sign or symptom of tumour has been defined in 1413 patients with breast cancer. The months of highest detection were in the late spring-early summer, and lowest detection was in late autumn-early winter. Analysis of subgroups indicates that this cyclic trend was most significant in younger women with small or moderate-sized tumours containing steroid hormone receptors, particularly progesterone receptors. It seems likely that this variation is related to the effect of cyclic hormonal changes on tumour growth, possibly mediated through the pineal.