Seasonal variations in the frequency distribution of breast cancer in Greek women according to the month of their birth.

The frequency distribution of patients with breast cancer according to the month of their birth was examined in 1,165 women comprising the total number of patients recorded in our cancer registry from 1975 until the end of 1982. Statistical evaluation of this material using an exact chi 2 for simple null hypothesis demonstrated the existence of two high frequency peaks corresponding to March and April in the spring and September in the autumn. These frequencies were significantly higher (P less than 0.001) than those of the remaining months. Confirmation of this finding would imply the introduction of a new variant in breast cancer epidemiology.