McDonald's CEO Steps Down Due to Cancer  SAN FRANCISCO (Reuters) - McDonald's Corp. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MCD.N target=/stocks/quickinfo/fullquote"&gt;MCD.N&lt;/A&gt; said on  Monday President and Chief Executive Charlie Bell had stepped  down to focus on his cancer treatment and that Vice Chairman  Jim Skinner would replace him.