Additional Study Information: The purpose of this study is to determine whether there is clinical benefit to continue therapy beyondprogression for metastatic or unresectable breast cancer. The treatment that is being investigated in this clinical trial, ribociclib (LEE011), is part of a family of oral medications (pills) that are called Cyclin Dependent Kinase 4 and 6 inhibitors, which are also referred to as CDK4/6 inhibitors for short. This family of medications targets the mechanism that drives the multiplication of cancer cells, and thus slows down the growth of tumors. Ribociclib and palbociclib (another CDK 4/6 inhibitor) are approved by the FDA to treat patients like you who have metastatic or unresectable breast cancer that is sensitive to hormones and which is not sensitive to the effects of the HER2 protein.