Merck's cancer immunotherapy finally hit a stumbling block in a pivotal study with lung cancer patients that caused the stock to slip 1.5% on Tuesday morning. It's more than a little surprising because Keytruda has been taking huge steps toward becoming the world's top-selling drug since Merck & Co. (NYSE: MRK) revealed game-changing lung cancer trial results in 2016.
During a study with small cell lung cancer that hadn't received any treatment for their disease before, adding Keytruda to standard chemotherapy failed to produce a significant overall survival benefit.
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