AstraZeneca shares fell as much as 7.7% on Monday after reports that the company had held preliminary discussions with Bristol Myers Squibb (BMS) over a possible merger, triggering a sharp investor selloff amid concerns about the strategic and financial merits of such a combination. Based on Friday's market close, AstraZeneca was valued at approximately $264.1 billion, while Bristol Myers Squibb had a market capitalization of about $133.4 billion, giving the two companies a combined market value of nearly $400 billion. Bristol Myers Faces Revenue Pressure From Patent ExpirationsFor Bristol Myers Squibb, the reported discussions come as the company prepares for the loss of exclusivity on several of its largest products over the coming years, a challenge the company has identified in filings with the U.S. Securities and Exchange Commission (SEC). Oncology Overlap Could Face Intense Regulatory ScrutinyAny transaction involving AstraZeneca and Bristol Myers would likely undergo extensive antitrust reviews in multiple jurisdictions because both companies maintain significant positions in global oncology markets. Investors will likely focus on any future statements from AstraZeneca or Bristol Myers Squibb regarding their strategic priorities.