Today's biggest winners and losers in the stock market.

On this episode of Stock Movers:
- Shares of Gilead Sciences (GILD) slipped in premarket trading after the company agreed to buy biotech firm Arcellx Inc. (ACLX) in a deal with an equity value of up to $7.8 billion as the US drugmaker seeks to boost its cancer drug pipeline. Gilead, which owns 11.5% of Arcellx’s outstanding stock, will pay $115 per share in cash, with a contingent payment of $5 per share dependent on future sales, according to a statement Monday. The price is almost double Arcellx’s closing price on Friday.
- Shares of Merck & Co. (MRK) rallied ahead of the US market open after the Wall Street Journal reported the company plans to split its main pharmaceutical unit in two as it prepares for the approaching patent expiry of its best-selling drug. The US drugmaker will separate its human-health division into a business that will house its cancer medications — including blockbuster immunotherapy Keytruda — and another for its non-cancer therapies, such as the HPV vaccine Gardasil, the newspaper reported.
- Shares of Domino's Pizza (DPZ) jumped premarket after the company reported a larger-than-expected rise in comparable sales, as consumers were drawn to the pizza chain’s budget-friendly pies. The Ann Arbor, Michigan-based company made more money by selling more food to its stores, charging higher prices for ingredients and collecting more fees from franchise operators for advertising and royalties, it said in a Monday statement.