"Gynecomastia represented the principal drawback of tE2, occurring in 85% of patients in that group compared with 42% of those receiving LHRH agonists, with grade 2 or higher events in 37% compared with 9%. Prophylactic breast irradiation, used in only 8% of tE2 patients, did not appear to meaningfully reduce gynecomastia rates."
https://www.targetedonc.com/view/estradiol-patch-matches-standard-hormone-therapy-in-locally-advanced-prostate-cancer-phase-3-trial-finds