Merger talks between AstraZeneca and Bristol Myers Squibb have created one of the year’s biggest pharmaceutical stories. A combination would unite major positions in oncology, rare diseases, neuroscience and cell therapy.

AstraZeneca shares fell as investors questioned the price, financing and regulatory obstacles. Bristol Myers could attract support if traders expect a meaningful premium.

Why the story matters

AstraZeneca has built a strong growth profile around cancer drugs and rare-disease treatments. Bristol Myers offers a large US commercial network, established oncology products and valuable cell-therapy assets.

A merger could create savings and expand research, but it could also increase debt and distract management. AstraZeneca’s Imfinzi and Bristol Myers’ Opdivo compete in cancer immunotherapy, raising anti ...