I have ER/PR+ HER2- breast cancer. My understanding is ER+ breast cancer means the cancer cells have estrogen receptors that can bind with estrogen to promote cancer cell growth. Even if the estrogen disappears in the body due to Femara, the cells could still have the estrogen receptors making it ER+. Could your breast cancer have randomly mutated into triple negative? I take Kisqali (inhibits CDK 4/6 proteins that help cancer cells divide) and Letrozole (reduces the amount of estrogen produced in the body). It's been working for me for over 2 years. I haven't had another biopsy since we removed the cancer down to a level of not being able to view it on scans. It's just a wait and see for me. My cancer is super aggressive this time so let's hope the meds keep working and my cancer doesn't further mutate. Best of luck to you.