I have ER+ breast cancer and am 15 months post mastectomy, 6 node removal (3 positive) and 16 proton radiation treatments. Surgery in 4/21. I am taking 20 mg of tamoxifen and have daily headaches that I try to ignore. I had a cording issue that PT resolved and now a pectoral muscle/shoulder issue that, again, PT is helping. Otherwise, I am back to normal. I am about to be 83. My Mayo oncologist never mentioned another drug, but I did have a genetic test to confirm that I was properly metabolizing tamoxifen. Good luck to you. Hope surgery and follow up treatment goes well.