This randomized phase II trial studies how well two doses of carfilzomib work with dexamethasone in treating patients with relapsed or refractory multiple myeloma. Carfilzomib may stop the growth of cancer cells by blocking some of the enzymes needed for cell growth. Drugs used in chemotherapy, such as dexamethasone, work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Giving carfilzomib together with dexamethasone may kill more cancer cells.
The purpose of this study is to see if taking metfomin can affect some of the risk factors associated with breast cancer, such as breast density, certain proteins and hormones, certain metabolites produced in the body, body weight, waist and hip sizes.