Immunomedics Shares Drop 53%

Shares of Immunomedics Inc. lost more than half their value Tuesday after Amgen Inc., the world’s largest biotechnology company, said it would not proceed with new tests of an experimental cancer medicine the firms were developing.

Thousand Oaks-based Amgen, which licensed the drug in 2000, will return it to Immunomedics or try to sell its rights to another party, Amgen spokeswoman Trish Hawkins said.

The companies stopped a test of the drug earlier this year. Both said at the time that new medicines -- approved after the trial began -- also were designed to treat patients with non-Hodgkin’s lymphoma who no longer responded to older treatments.

Shares of Morris Plains, N.J.-based Immunomedics shares fell $3.87, or 53%, to $3.38 on Nasdaq, a seven-month low. Amgen slipped 16 cents to $58.98.