Amgen Inc. said Thursday that it discontinued a key clinical trial of colon cancer treatment Vectibix after discovering that the drug reduced chances of survival.
Amgen said an interim look at the trial found that colon cancer patients treated only with chemotherapy and Avastin, a biologic cancer drug sold by Genentech Inc., were more likely to live than patients who also received Vectibix.
"The fact that the drug had a negative impact on survival is shocking," said Geoffrey Porges, an analyst at market researcher Sanford Bernstein.
Shares of the world's largest biotechnology company, down about 13% year to date, fell nearly 5% in after-hours trading.
The stock's outlook was already clouded by recent medical studies linking anemia drugs, which account for more than half of Amgen's sales, to a higher risk of stroke, heart attack, blood clots and even death in certain patient groups.