Binge Drinking and Risk of Breast Cancer: Results from the SUN ('Seguimiento Universidad de Navarra') Project.

Alcohol intake is associated with the risk of breast cancer. Different patterns of alcohol-drinking may have different effects on breast cancer even when keeping constant the total amount of alcohol consumed. We aimed to assess the association between binge drinking and breast cancer risk. The SUN Project is a Spanish dynamic prospective cohort of university graduates initiated in 1999. In the 556-item lifestyle baseline questionnaire a validated food-frequency questionnaire was embedded. Participants completed biennial follow-up questionnaires. Cox regression models were used to estimate the hazard ratio (HR) for breast cancer associated with the exposure to binge drinking. A stratified analysis was performed according to menopausal status. We included 9577 women (mean age = 34 years, SD = 10 years), with a median follow-up of 11.8 years. Among 104,932 women-years of follow-up, we confirmed 88 incident cases of breast cancer. Women in the binge drinking group showed a higher risk of breast cancer (HR = 1.76; 95% CI: 1.03-2.99) compared to women in the non-binge drinking category. In the stratified analysis, a 2-fold higher risk for premenopausal breast cancer was associated with binge drinking habit (HR = 2.06; 95% CI: 1.11-3.82). This study adds new evidence on the association of binge drinking with breast cancer risk.