Studies included in this review were identified primarily from a PubMed search targeting GnRH agonist (goserelin OR leuprolide/leuprorelin) AND breast cancer AND long-acting (3-month OR 12-weeks OR 6-month OR 24-weeks) AND efficacy and screened for relevancy, supplemented with additional unpublished study data available in the public domain. This evidence concerns the gene GNRH1 and breast cancer.