Jim Cramer said Friday that he was shocked after Bristol-Myers Squibb announced its lung cancer drug failed in a late-stage study.
Shares of Bristol-Myers dropped more than 17 percent Friday morning while competitors, such as Merck with different versions of the cancer therapy, rose.
The drug, Opdivo, failure comes as a surprise because it has been approved to treat other types of cancer. Lung cancer is the leading cause of cancer death in the United States, according to the Center for Disease Control and Prevention.
"This was the hottest drug in our era, arguably," Cramer told CNBC's "Squawk on the Street." "I am stunned because the success rate of this drug has been amazing."
He added, peak revenues for the drug could have been around $12 billion to $15 billion.
SunTrust Robinson Humphrey downgraded Bristol-Myers' shares to "neutral" from "buy" after the news.