Additional Study Information: The purpose of this study is to determine whether there is clinical benefit to continue therapy beyond progression 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.