My Husband Had Aggrosive Prostate Cancer. He Had An Operation

my husband had aggrosive prostate cancer. he had an operation and it was removed, but the doc. said it was starting to spread outside of the prostate. As for as I know he removed everything he could see. He order lump note check (17) and they where all clean. and the surrounding tissus was tested and had no cancer. Then a wask done 3 wks later and the pst test came back with a score of 2.5. it should have been zero. Well the doc. has sent him to a radialagiest and he is going to do any othe pst test. but he said even if it comes back zero. \my husband should have homon and radiation treatment because he is at a high risk of it returning. When he was operated on the doctor and scored him a 7/10 glease score but, when he operated he classed it as a sa9/10 gleason score.
My question is: if the pst comes back as "0" that means he has no cancer. Why be aggrasive by giving hormons and readiation? I could see readiation, but why hormones. and put him through the side effect if he does not have cancer and this is a prevention treatment?