@ginny100 I've been taking Kisqali (CDK 4/6 inhibitor) and Letrozole (AI) for 3+ years now due to my highly aggressive recurrent breast cancer considered stage 4. I had the chest wall tumor removed (mastectomies the first time), positive margin then radiation. They also believe cancer cells got away to other parts of my body before the surgery due to aggressive nature (Ki-67 50%), but so far so good with clear scans. Next round of CT scans in a week. My oncologist told me that Kisqali, Ibrance and Verzenio clinical trials all showed an increase in progression free survival, but only Kisqali showed an increase in overall survival time (median time nearly a year) and that is why he chose Kisqali. The one issue Kisqali has that the others don't is a risk for QT prolongation, a deadly heart rhythm, but only 4% of women get it. It happened to me immediately on 600 mg. We stopped the med, my heart rhythm returned to normal and I'm now on the 400 mg. Kisqali is very expensive. Group insurance I had was great, but once I stopped working and went on Medicare, it would have been $14000/yr. copay so I was eligible for the Novartis PANO assistance and pay zero now. No more QT prolongation, but I have had ongoing issues with afib anywhere from 1-4 times a month since I've been on it. Maybe I was prone to afib because I did have it once years earlier. The other side effects I've had with these two meds are significant fatigue, hair thinning, constipation (that greatly improved after year 1), low BP/heart rate, increased pain from my pre-existing neuropathy. Letrozole has caused joint pain and very challenging insomnia. I'm willing to tolerate the side effects because so far so good on CT scans. I plan to continue on these meds as long as they work. I had osteopenia before starting the meds. I have my two year DEXA scan due in July and hopefully the osteopenia hasn't progressed. I started a third cancer med for non-related lung NETs (neuroendocrine lung cancer) two months after these and that med also causes fatigue, hair thinning and low BP/HR so hard to break it all down by med sometimes. Prayers for your decision and success.