New York CNN  —  US stocks tumbled Thursday morning after the latest GDP report showed that US economic growth slowed to 1.6% in the first quarter of the year, a much weaker pace than expected. The Dow opened 500 points, or 1.3%, lower; the S&P 500 was down 1.3% and the Nasdaq Composite slid by 2.1%, as investors projected a longer wait for the first rate cut from the Federal Reserve. This is a developing story and will be updated.