Pfizer, the world's second largest drugmaker, says the drug prevented breast cancer from getting worse for more than 20 months, in a trial involving 165 patients.
Current medications do so for about 10 months.
The drug, Palbociclib, targets specific proteins to block tumors. It will likely undergo broader testing with more patients before the FDA approves it. Although the FDA sometimes accelerates approval for drugs that show promise.
The outcome wasn't as positive as some initial results reported earlier in the tests, said University of Michigan business professor Erik Gordon, who studies the biomedical industry but isn't affiliated with the trial.
But, he added, "there's been a lot of hope surrounding this class of cancer drugs, and this keeps that hope alive."
The results were presented by the lead researcher, Dr. Richard S. Finn, associate professor of medicine at UCLA, during the annual meeting of the American Association of Cancer Research in San Diego.
The Associated Press contributed to this report