Cetus won a patent on a potential cancer drug.

The biotechnology company said the U.S. Patent and Trademark Office approved its application for protection of a genetically altered version of a protein that occurs naturally in the human body, Interleukin-2. The patent is the first ever on such a substance. Cetus, based in Emeryville, Calif., has been testing the drug since March on patients with Acquired Immune Deficiency Syndrome, or AIDS, and with various types of cancer. Cetus said it could be selling treatments for such diseases by 1988.