If you choose to join this study, you will be randomly assigned (like a coin flip) to 1 of 2 groups: Group One If you are in this group, you will get the study drugs neratinib and palbociclib. You will get neratinib as pills you take by mouth once every day, and palbociclib as pills you take by mouth every day for 21 days, followed by 7 days off. You will start this study regimen taking neratinib alone. Over the first two weeks of treatment, you will gradually increase the dose you take. On week three, you will start taking the full dose of neratinib and you will also start taking palbociclib on the schedule described above. You will take neratinib and palbociclib for as long you as you and th study doctor believe that your are benefitting. Group Two If you are in this group, you will get the study drug neratinib. You will get this drug as a pill you take by mouth once every day. Every 28 days of this treatment is called a cycle. Over the first two weeks of treatment, you will gradually increase the dose you take.