Hi, if he started hormone treatment in January then it is too late for him to try RT to the breast buds, the only treatment that can sometimes prevent breasts from growing. However, he could ask his oncologist, specialist nurse or GP whether they are prepared to give him a prescription for tamoxifen which may slow down the breast growth now.
Stopping HT now might be unpopular with his specialist as the accepted thinking is that the longer he is on HT the more likely the RT is to work, and his PSA was so high at diagnosis that you probably shouldn't take any risks. There has been some new research though to suggest that HT makes no difference to the outcome in some cases so it is worth a conversation with the medics.