U.S. stocks rallied on Tuesday, with the S&P 500 on track for a fourth straight session of gains boosted by strong corporate results, including Apple's.

Synergy Pharmaceuticals (SGYP) is getting some much-needed love with phase 2 data, presented at a medical meeting on Monday, for the company's lead drug candidate, plecanatide in Irritable Bowel Syndrome (IBS-C).