When the cancer tests have resulted in the Doctor announcing that the cancer is hormonal sensitive. This can be true in a small percentage of breast or prostate cancer.
If the doctors have not mentioned "hormone sensitive," by all means ask. Many times medical doctors are too busy to volunteer any details, so ask.
Generally it is always good to bring an advocate with you whenever you visit a doctor.
PEP contains some glandulars to assist with healing. In the case of a hormonally sensitive cancer glandulars could stimulate cancer growth.