I don't think it's unusual for Merck to wait to PR results until they are presenting them at an appropriate conference which, in this case, I assume will be ASCO. fwiw, MRK let ARIA PR the endometrial results as well.
You could be right of course, though I wouldn't think a general top-line PR would be an issue prior to their presenting at a major conference. Do we know how MRK has reacted in similar situations before with respect to other drugs partnered with other biotechs?