A substance being studied in the treatment of some types of cancer. Yttrium Y 90 SMT 487 contains yttrium Y 90 (a radioactive form of the metal yttrium) attached to a molecule that binds to certain types of neuroendocrine tumors (tumors that come from cells that release hormones). The radioactivity from yttrium Y 90 may kill the cancer cells. Also called yttrium Y 90 DOTA-tyr3-octreotide and yttrium Y 90 edotreotide.