MARGetuximab Or Trastuzumab (MARGOT)

The purpose of this study is to determine how well participants with stage II-III HER2-positive breast cancer respond to pre-operative treatment using one of two different combinations of drugs. Drugs and Combinations used: * Paclitaxel, Pertzumab and Margetuximab (Margenza) * Paclitaxel, Pertzumab and Trastuzumab (Herceptin)

This is a randomized open-label phase II trial comparing paclitaxel/margetuximab/pertuzumab (TMP) to paclitaxel/trastuzumab/pertuzumab (THP) in patients with anatomic stage II-III HER2 positive breast cancer. * The research study procedures include screening for eligibility and study treatment including laboratory evaluations, two mandatory research biopsies and follow up visits. * Participants will be randomized, which means randomly assigned, to one of two treatment arms. The treatment arms in this study and the names of the study drugs in each arm are: * Arm A: Paclitaxel, Pertzumab and Margetuximab * Arm B: Paclitaxel, Pertzumab and Trastuzumab Participants will receive study treatment for 12 weeks prior to surgery and will be followed for 10 years after surgery. After surgery, some participants will continue to receive the study drug margetuximab for a year in total, if they respond very well to the first 12 weeks of treatment with margetuximab. It is expected that about 171 people will take part in this research study. This research study is a Phase II clinical trial. Phase II clinical trials test the safety and effectiveness of an investigational drug combination to learn whether the drug combination works in treating a specific disease. "Investigational" means that the drug combination is being studied. The FDA (the U.S. Food and Drug Administration) has approved paclitaxel, trastuzumab (Herceptin), and pertuzumab as part of a pre-operative treatment option for stage II-III HER2-positive breast cancer. The U.S. Food and Drug Administration (FDA) has approved margetuximab (Margenza) for advanced HER2-positive breast cancer.