It seems like there’s some confusion here about exactly what medication you are talking about. I’m gathering you are talking about HRT which increases hormone levels and would continue to feed any potential cancer. It sounds like some think you are talking about aromatase inhibitors which would stop the growth. Personally I would discontinue any use of HRT and monitor the breast. A mastectomy would not be any guarantee so I don’t think you should be second guessing that. People can still have a reoccurrence even after a mastectomy. Cancer can show up in the scar tissue or just go right to the ribs.