TheraSphere® is a humanitarian use device (HUD) for treating cancer that originates in the liver. TheraSphere® consists of millions of tiny glass beads containing radioactive yttrium-90. The glass radioactive beads (20-30 micrometers in diameter – about a third of the width of a human hair) are delivered directly to the liver tumors. It can be used to downstage tumors to become eligible for surgery or transplantation. It is also the only medical device approved in the United States to treat primary liver cancer patients with portal vein thrombosis (PVT). TheraSphere® has been approved as an HUD based upon its safety and probable benefit.