Pfizer said on Tuesday it was halting a late stage study of its experimental drug for advanced melanoma after data showed it was no better than standard chemotherapy.
The latest disappointment for the world's biggest drugmaker sent its shares down about 2 percent in after-hours trading.
Pfizer said researchers will work with their patients to determine if they are benefiting from treatment with the drug, tremelimumab, and should therefore continue treatment.
But its review of interim data from the phase 3 trial found that it ultimately would not demonstrate superiority to standard chemotherapy, leading to the decision to discontinue the study. Phase 3 is typically the final stage of human testing before a drug is submitted for an approval decision.
"Although this outcome is disappointing, Pfizer remains committed to investigating new treatment options for patients with melanoma, a high risk area of research with significant unmet medical need," Charles Baum, who heads Pfizer's oncology therapeutic area, said in a statement.
The company said full data from the phase 3 study was being analyzed and would likely be made available at a major cancer meeting in June.
Pfizer said it was not abandoning tremelimumab.
"We continue to focus on additional studies involving tremelimumab alone and in combination with other therapies which are currently ongoing in patients with several types of cancer," Baum said.
"We will continue to assess the study data to understand the clinical benefit seen in some patients who received tremelimumab," Baum added.
At its meeting with analysts and investors last month Pfizer said it was making oncology one of its priorities, establishing a new separate unit for cancer drugs.
Pfizer has suffered a series of disappointments in recent years, including the spectacular clinical failure of the cholesterol drug it hoped would one day replace its $12 billion a year cash cow Lipitor, and the commercial failure of its now abandoned inhaled insulin product.
Pfizer shares slipped to $20.90 in extended trading from their New York Stock Exchange close of $21.38, before recovering to $21.05.