I am NOT a physician, and am actually a fairly new member here. Learning tons from this site. It is my understanding, after treatment (radiation therapy) IF you also have some BPH, HRT can aggravate the BPH causing prostate enlargement to some degree. This could cause your PSA to increase somewhat. That is why it is important to be followed by a good urologist who will do regular digital rectal exams, (feeling for lumps or bumps that were not there previously, but also can tell if your prostate has enlarged more (which explains the PSA increase) IF your urologist does feel a lump or bump or anything unexplained by your treatments, he can order a biopsy, or perhaps and MRI to image the prostate and rule out for additional problems. The data is pretty clear, HRT does not cause prostate CA. One thing to keep in mind, radiation therapy takes time work. It is the impact of the total dose of radiation, over time, even after the initial treatment period that eventually kills the CA and also causes scaring to occur in the prostate of healthy tissue. It may not have completely killed the cancer if you re started HRT too soon.