AstraZeneca and Bristol Myers Squibb never held merger discussions and are not in talks now, a senior source close to the matter told Reuters on Wednesday. AstraZeneca shares dropped roughly 9% in the wake of the deal reports, while Bristol Myers Squibb shares weathered the news with relatively little movement. Bristol Myers Squibb stock rose 6% in U.S. premarket trading. Cancer drugs accounted for more than 40% of Bristol Myers Squibb sales through the first six months of 2026. Before Monday's session, AstraZeneca carried a market capitalization of $264 billion, while Bristol Myers Squibb's stood at roughly $133 billion.