Buffett Cancer Diagnosis Has Analysts, Investors Scrambling

A number of issues also arise for mutual funds that hold Berkshire Hathaway in their portfolios.

"There are a number of funds that own this stock where it's not only a top 10 holding, but also 8,9 or 10% of the portfolio," S&P Capital IQ mutual fund analyst Todd Rosenbluth told AdvisorOne. "The company is well-liked because it is so well-run. It's also a financial services company, but it's a diversified holding because of the other companies it owns, more so than, say, Coca-Cola. Lastly, fund managers have bought into Buffett's management style, and believe it will deliver solid returns for the foreseeable future."

It is this last point, Rosenbluth said, that is most affected by the diagnosis and announcement.

"You have a class of funds that have over $1 billion in assets and only have 40 or so stocks," he said. "These include funds like Clipper, Fairholme and Sequoia. Berkshire Hathaway is a top 10 holding in a concentrated portfolio, so any negative news about the stock will disproportionately affect the portfolio."

As a result, Rosenbluth concludes, investors should evaluate whether or not that mutual fund should continue to be a core holding in light of the fact that the portfolio now has additional risk.