Stage IV Breast Cancer

The purpose of this study is to test different doses of abemaciclib to find the best dose in participants while receiving hormone therapy and radiation therapy.

The purpose of this preliminary research study is to see if patients discontinuing maintenance Herceptin and/or other anti-HER-2 treatments with monitoring in addition to radiologic imaging and routine blood work will stay in complete radiological remission and to determine how long patients are able to stay in complete radiological remission without treatment.

The purpose of this study is to test the safety and effectiveness of a sequence of drugs (a Taxane plus Trastuzumab plus Pertuzumab followed by Trastuzumab Deruxtecan, followed by Tucatinib plus Ado-Trastuzumab Emtansine (T-DM1), followed by Trastuzumab plus Pertuzumab plus Tucatinib) in HER2+ Breast Cancer. The study will help investigators understand whether first intensifying therapy for a specific period and then stopping treatment is safe and effective for participants. The names of the study drugs involved in this study are: * Paclitaxel (a type of anti-microtubule agent) * Docetaxel (a type of anti-microtubule agent) * Nab-Paclitaxel (a type of anti-microtubule agent) * Trastuzumab (a type of IgG1 kappa monoclonal antibody) * Pertuzumab (a type of monoclonal antibody) * Trastuzumab Deruxtecan (a type of HER2-directed antibody drug conjugate) * Tucatinib (Tyrosine Kinase HER2 Inhibitor) * Ado-trastuzumab emtansine or T-DM1 (a type of HER2-targeted antibody-drug conjugate)