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Merck shares slip as Keytruda fails another clinical trial

Wallace Witkowski

Merck & Co. shares slipped in the extended session Monday after the drug maker said its cancer treatment Keytruda failed to meet clinical endpoints in another late-stage study. Merck shares declined 0.7% after hours, following a 0.2% rise to close the regular session at $78.88. In a Phase 3 clinical study, Merck said Keytruda "did not meet its pre-specified primary endpoint of superior overall survival" compared with chemotherapy in a subset of breast cancer patients. In late April, Merck said Keytruda did not show significant improvement over chemotherapy in gastric cancer patients. For the year, Merck shares are up 3.2%, compared with a 13.3% rise in the S&P 500 index .