* Mallinckrodt to buy Questcor for $5.6 bln
* MannKind stumbles; FDA extends review date for insulin treatment
* Futures off: Dow 57 pts, S&P 8.25 pts, Nasdaq 29 pts
By Chuck Mikolajczak
NEW YORK, April 7 (Reuters) - U.S. stock index futures fell on Monday, putting the S&P 500 on track for its third straight decline, after weakness in momentum names sent the Nasdaq and benchmark S&P index to their worst drop since February in the prior session.
* Declines in momentum names such as Netflix Inc and TripAdvisor Inc overshadowed the relatively strong March payrolls report on Friday, leaving investors anxious about how much further they may fall. Facebook Inc lost 1.1 percent to $56.14 in premarket trade.
* Earnings season gets under way this week, with earnings expected from financials JPMorgan Chase & Co and Wells Fargo & Co, as well as retailer Bed, Bath & Beyond expected.
* S&P 500 companies' first-quarter earnings are projected to have increased just 1.2 percent from a year ago, Thomson Reuters data showed. The forecast is down sharply from the start of the year, when growth was estimated at 6.5 percent.
* A lackluster first-quarter earnings season impacted by harsh winter weather could spark a pullback, according to some analysts, with investors looking for optimism for the second quarter.
S&P 500 e-mini futures fell 8.25 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures lost 57 points and Nasdaq 100 futures declined 29 points.
* Specialty pharmaceuticals company Mallinckrodt Plc agreed to buy drugmaker Questcor Pharmaceuticals Inc for about $5.6 billion to gain access to its multiple sclerosis drug, Acthar Gel. Questcor shares surged 34.1 percent to $91 while Mallinckrodt rose 10.4 percent to $69 in premarket.
* MannKind Corp slumped 11.9 percent to $6.05 before the opening bell. The company said the U.S. Food and Drug Administration extended the review date of its inhaled insulin treatment by three months.
* Pfizer Inc shares fell 2.1 percent to $31.50 in premarket trade. The company's experimental breast cancer drug in a clinical trial nearly doubled the amount of time patients lived without their disease getting worse, but overall survival was not yet shown to be statistically significant, researchers said.
* European stocks dropped, halting a three-week rally and tracking the selloff on Wall Street on Friday.
* Japanese shares were hit on Monday by a one-two combination of a higher yen and a selloff in the tech sector. (Reporting by Chuck Mikolajczak; Editing by Nick Zieminski)