Because Genentech is a leading developer of cancer therapies, some doctors also fear that the company's pricing plans for Avastin - around $8,800 a month - may encourage other companies to charge more for their own oncology drugs.

Volatility may be rising simply because investors must digest more information every day.

Every public company depends to some extent on the trust of its investors.

Companies buy customers when they cannot win new business on their own. They merge when their executives do not have a better idea of what to do.

The details of the personal expenses that executives put on the company tab often are not known because loopholes in federal disclosure rules let publicly traded companies generally avoid disclosing the perks they give executives along with pay and stock options.

As they grow, companies saturate their markets, become more complex and difficult to manage, and face larger and more entrenched competitors.