Is a woman's date of birth related to her risk of developing breast cancer?

Some previous reports have shown seasonality in the date of birth in patients with breast cancer, others have not. In this study of 1,110 women with unilateral breast carcinoma significantly more cases had been born in the first than the second half of the year. This finding could, however, not be linked to the later development of breast cancer as their case-matched controls showed a similar trend. These results underline the importance of using relevant control material in such studies.