c&en, chemical & engineering news, august 13, 2020. Astatine is the rarest naturally occurring element on Earth. It resists easy chemical classification. In reactions, it sometimes acts like a halogen, sometimes like a metal. But astatine isn’t just a chemical curiosity. Groups around the world are investigating the isotope astatine-211 as a potential cancer treatment. Astatine-211 can be produced from an inexpensive, non-enriched bismuth target; it can be attached to small molecules or antibodies; and it has lower side-effect risks than some other therapeutic isotopes. Early clinical studies are showing promise for cancer therapy and pre-transplant immunoablation. Read more >>