ESR1 and Gynecomastia: The following search terms were used: “gynecomastia,” “breast enlargement,” “mastodynia,” “breast pain,” “breast event*,” “bicalutamide,” “antiandrogen*,” “SERM*,” “selective estrogen receptor modulator*,” “tamoxifen,” “clomiphene,” “aromatase inhibitor*,” “aromatase inhibition,” “anastrozole,” “radiotherapy,” and “breast irradiation.” Boolean AND/OR operators were applied to combine these terms appropriately.