Breast cancer is most often diagnosed in spring and fall, especially in areas the farthest from the equator, according to a study of 2,921,714 breast cancer cases across 64 global regions and published in the journal Breast Cancer Research and Treatment (February, 2010).
These data make it clear that human breast cancer discovery occurs non-randomly throughout each year with peaks near both equinoxes and valleys near both solstices. This stable global breast cancer seasonality has implications for better prevention, more accurate screening, earlier diagnosis, and more effective treatment. This complex latitude-dependent breast cancer seasonality is clearly related to predictable local day/night length changes which occur seasonally. Its mechanism may depend upon seasonal sunlight mediation of vitamin D and seasonal mediation of nocturnal melatonin peak level and duration.