Benzinga's Top #PreMarket Gainers

Merrimack Pharmaceuticals MACK shares jumped 73.12% to $7.60 in pre-market trading after the company reported that MM-398 has achieved primary endpoint of overall survival in Phase 3 trial in post-gemcitabine metastatic pancreatic cancer. Weight Watchers International WTW surged 11.72% to $22.12 in the pre-market session after the company reported upbeat first-quarter results and raised its earnings forecast for the year. Yelp YELP shares gained 7.07% to $10.45 in pre-market trading after the company reported better-than-expected Q1 results. Analysts at Piper Jaffray upgraded the stock from Neutral to Overweight. DIRECTV DTV soared 6.44% to $82.60 in the pre-market trading on rumored AT&T T bid.