Background: The association between alcohol intake and breast cancer recurrence or development of second primary breast cancer in the survivor population is unclear. The aim of this systematic review was to evaluate the existing evidence to assess the extent to which alcohol consumption is associated with breast cancer recurrence and second primary breast cancer.

Methods: Six databases (Cochrane Library, EMBASE, MEDLINE, PubMed, Scopus and Web of Science) were searched using the following search phrase: (breast cancer OR breast adenocarcinoma OR breast neoplasm OR breast tumour) AND (alcohol^∗ OR alcohol intake OR alcohol consumption OR ethanol) AND (recurrence OR second primary). A narrative synthesis was conducted on studies meeting the inclusion criteria.

Results: After screening, 16 studies met the inclusion criteria, of which 11 assessed breast cancer recurrence and 5 assessed second primary breast cancer. Considerable clinical and methodological heterogeneity was observed between studies. Approximately half of the included studies observed a modest, but significant, association between alcohol consumption and increased risk of breast cancer recurrence or development of a second primary breast cancer, with some studies observing associations from as little as six grams of alcohol intake per day. Two studies suggest this association was stronger in postmenopausal women.

Conclusion: There is some evidence that alcohol consumption increases the risk of breast cancer recurrence, particularly in postmenopausal women. The association between alcohol and development of a second primary breast cancer is less clear. Inconsistencies in methodology and results across studies complicate attempts to develop a cohesive interpretation of findings.