A substance being studied in the treatment of breast cancer that has spread to other parts of the body. It is also being studied in the treatment of other cancers and conditions. GC1008 binds to a protein called transforming growth factor-beta (TGF-beta), which is found on some cancer cells. GC1008 may help keep cancer cells from growing and prevent the growth of new blood vessels that tumors need to grow. It is a type of monoclonal antibody and a type of antiangiogenesis agent. Also called anti-TGF-beta monoclonal antibody GC1008 and fresolimumab.