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David Brennan's move to retire as AstraZeneca's (NYSE:AZN) CEO in June did not come as a surprise to those who had been urging for a change at the top over the company's drug development shortcomings. In an industry that walks a tightrope between innovation and regulation and the financial considerations that frame them, there are two critical characteristics that can undermine a CEO:being too bold or not bold enough. Brennan was a bit of both.

His leadership was bookended by two acquisitions -- a $15.2 billion deal for MedImmune, a drug developer with a focus on influenza vaccines and the $1.26 billion purchase of biotechnology business Ardea Biosciences.