If we’ve learned anything about the exciting new world of immunotherapy cancer drugs it’s this: It’s a fluid landscape and fortunes can shift on a dime. Just ask Merck & Co. ( MRK ). Its drug Keytruda was overshadowed by Opdivo, the rival drug from Bristol-Myers Squibb ( BMY ) until last summer. That’s when Bristol’s drug disappointed in a big lung cancer study , which opened the door for Merck. And now Merck is looking for new ways to capitalize on Keytruda, including collaborating with Incyte ( INCY ).