AstraZeneca stock fell sharply on Monday as investors reacted negatively to that the British pharmaceutical company held merger discussions with Bristol Myers Squibb. On the other hand, BMY stock rose in premarket trading as the potential transaction generated optimism among Bristol Myers shareholders. Meanwhile, Bristol Myers Squibb shares climbed by in US premarket trading. AstraZeneca Shareholders Question Strategic BenefitsThe decline in AstraZeneca stock could be due to concerns that the company has little need for a transformative acquisition of this size. Bristol Myers has faced some pressure from upcoming patent expirations and competition affecting some of its major medicines.