NEW YORK Mon Apr 28, 2014 5:31pm EDT (Reuters) – The S&P 500 ended higher on Monday after a volatile session, as gains in Apple and Pfizer helped offset another round of selling in some high-growth tech shares. The Dow also managed to end the session with a modest gain, while the Nasdaq closed slightly lower after rebounding from a fall of over 1 percent. Leading the Nasdaq down was Amazon.com, which extended Friday’s sharp […]