Entering into a collaboration with a pharmaceutical giant like Merck for a Phase 1 trial not only validates Ideaya Biosciences' research but also potentially enhances its market position and investor confidence, likely leading to a positive short-term impact on its stock price.

For Merck, this collaboration represents an expansion of its oncology portfolio, particularly in endometrial cancer treatment. While the impact on Merck might be less pronounced due to its larger size and diversified portfolio, the partnership is still a positive development, likely contributing to a slight uptick in its stock price in the short term.