In the first portion of the study, the investigators will examine which dose of eribulin is the safest when given in combination with pertuzumab and trastuzumab. For the first 6 participants enrolled onto the study,the investigators will be looking to see if the standard dose of eribulin can be administered safely with standard doses pertuzumab and trastuzumab. If this dose of eribulin is not tolerated well, the investigator will test the three-medication combination with a lower dose of eribulin. The highest dose that will be found to be safe will be used in the next participants. The dose the patients receive will depend on the number of participants who have been enrolled in the study before and how well they have tolerated their doses.