This trial studies how well the drug tucatinib works when given with trastuzumab deruxtecan. It will also look at what side effects happen when these drugs are given together. A side effect is anything a drug does besides treating cancer. Participants in this trial have HER2-positive (HER2+) breast cancer that has either spread to other parts of the body (metastatic) or cannot be removed completely with surgery (unresectable). All participants will get both tucatinib and trastuzumab deruxtecan.

This study looks at how safe and effective the study drug, atezolizumab, is when given with paclitaxel. To do this, they are comparing the treatment regimen with and without the study medication.

This study looks at how safe and effective the study drug, atezolizumab, is when given with paclitaxel. To do this, they are comparing the treatment regimen with and without the study medication.

This study is evaluating the efficacy and safety of nivolumab compared to placebo when given with neoadjuvant (pre-surgery) chemotherapy and adjuvant (post-surgery) endocrine therapy in participants with high-risk, estrogen receptor-positive, human epidermal growth factor receptor 2-negative (ER+, HER2-) early-stage breast cancer.