For example, a Danish population-based case–control study of 60 360 women with breast cancer26 and a US database cohort study of 914 such cases27 reported an 18%–62% increased risk of breast cancer, respectively, with exposure to prolactin-increasing antipsychotics, but only 2%–9.7% of the women had schizophrenia/bipolar disorder. This evidence concerns the gene PRL and bipolar disorder.