I'm 64 and was diagnosed with left breast invasive ductal carcinoma (ER+ HER2-) in Sept. 2020. It was caught early. Decided on bilateral mastectomy (personal choice and not something my breast specialist suggested). 23 lymph nodes removed with 3 showing cancer. I had 6 weeks of radiation but no chemo since Mammaprint showed no benefit from it. Started taking Letrozole (aromatase inhibitor) and took it for 3 years with regular 6 month exams from breast surgeon and oncologist. Labs were monitored and my markers never changed. In July 2023 I started experiencing some lower back pain. PCP prescribed steroids and muscle relaxers, along with stretching, thinking that I had probably pulled something in my lower back. Just happened to have one of my regular visits scheduled in August to see my breast specialist and she suggested having some scans run just to be safe. Scans came back kind of questionable so she scheduled a PET scan. Turns out my breast cancer had metastasized to my bones and was especially present in my spine. The PET scan showed a kind of shotgun effect with most bones in my body being affected to some degree. Started new treatment plan in October after conferring with my oncologist and getting a 2nd opinion at MD Anderson. That treatment plan consisted of Verzenio 150 mg with 2 injections of Fulvestrant (estrogen receptor antagonist) and one injection of Xgeva (bone builder) once a month following the initial 3 bi-weekly injections during the load-up period. Had a few side effects with the worst being diarrhea. It became chronic and eventually caused ulcerative colitis. Even though the treatment plan was working well and had stopped the cancer from advancing I had to stop the Verzenio after almost 8 months and start taking anti-inflammatory/steroid meds for my UC. During that time I had labs and injections every month, PET scans every 3 months and opted in for 2 kyphoplasty procedures to help reduce the pain in my spine, both lumbar and thoracic regions. Had issues with insurance authorizing new medication (Ibrance) so I just started taking Kisqali last week after being off Verzenio for 5weeks. Verzenio, Ibrance & Kisqali are all CDK4/6 inhibitors so the Kisqali should continue to work, but the side effects are a little different as is the dosage requirement. All that being said, I feel better than I did 7-8 months ago and the pain I have is tolerable on the days that it bothers me. I pray the Kisqali will continue to do the job that the Verzenio did (and without diarrhea), but only time will tell - next PET scan will be in October. With all that being said, YES, breast cancer can metastasize even while on aromatase inhibitors. Make sure your care team uses scans in addition to lab work and physical exams as often as they will allow. My care team told me that wasn't necessary and that the cancer markers in my blood would be the tell-tale sign of advancement. Didn't happen that way and I ended up with stage IV breast cancer. I moved all my care and treatments to MD Anderson and I travel 4 hours to get there. Yes, it's inconvenient, but I feel I'm in much better hands than I was initially. Educate yourself and don't ignore what your body or your mind tells you. Despite all the negatives, there are many treatment plans that can work. Everyone's situation is unique. I hope your cancer journey is the best it can be and you find the care you need! Prayers to all!