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.
The company warned in January that early results from the Vectibix trial showed no benefit in adding the drug to a regimen of chemotherapy and Avastin and that it was seeing increased side effects such as infections and pulmonary embolisms.
Vectibix, approved last year for later-stage colon cancer patients whose tumors have spread despite chemotherapy, is viewed as a key medicine in the development pipeline of Thousand Oaks-based Amgen.
Some analysts had predicted eventual sales of as much as $2 billion a year, but those forecasts hinge on the drug's use in patients with earlier-stage cancer.
Vectibix competes with Erbitux, which is sold by ImClone Systems Inc. and Bristol-Myers Squibb Co.