Last week delivered some impressive gains across the large-cap landscape, and if you had any of these ten stocks in your portfolio, you probably had a pretty good week. Here's what drove the action between December 15 and December 19.

The Leaders

Rivian Automotive Inc. (RIVN) took the top spot with a 20.57% gain after the electric vehicle maker announced it's expanding hands-free assisted driving capabilities and rolling out new software updates that give drivers more control and customization across both Gen 1 and Gen 2 vehicles. The news caught analysts' attention too, with multiple firms raising their price targets on the stock.

Sandisk Corporation (SNDK) climbed 10.57% for the week, riding the coattails of Micron Technology Inc. (MU). Micron crushed first-quarter estimates and issued strong guidance, which lifted sentiment across the memory and storage sector.

Moderna Inc. (MRNA) gained 16.15% after announcing that CEPI would invest up to $54.3 million to help advance Moderna's H5 pandemic influenza vaccine candidate toward licensure. That's a meaningful vote of confidence in the company's pipeline beyond COVID-19 vaccines.

BioMarin Pharmaceutical Inc. (BMRN) jumped 14.64% on acquisition news. The biotech company announced an agreement to acquire Amicus for $14.50 per share in an all-cash transaction, valuing the deal at roughly $4.8 billion in total equity value.

Defense, Fintech, and Travel

Rocket Lab Corporation (RKLB) gained 12.10% after securing a massive $816 million prime contract to build a missile-defense satellite for the US Space Force. That's the kind of contract that changes the trajectory for a company.

Lumentum Holdings Inc. (LITE) rounded out the middle of the pack with an 8.77% gain for the week, though no specific catalyst was identified for the move.

Affirm Holdings Inc. (AFRM) surged 12.49% after the company's CFO, Rob O'Hare, announced during a fireside chat that Affirm has renewed its partnership with Amazon for approximately five more years. That's a huge relationship for the buy-now-pay-later platform, and investors rewarded the news.

Cruise Control

Carnival Corporation (CCL) gained 10.73% after reporting better-than-expected Q4 adjusted earnings per share and issuing fiscal year 2026 adjusted EPS guidance that came in above analyst estimates. Cruise demand remains strong, and Carnival is capitalizing.

Alcoa Corporation (AA) picked up 9.84% for the week, though no specific news drove the aluminum producer's gains.

Norwegian Cruise Line Holdings Ltd. (NCLH) rose 10.56% in sympathy with Carnival's strong earnings report. When the cruise sector gets good news, the rising tide tends to lift all boats, and Norwegian benefited from the positive sentiment washing across the industry.

So there you have it: ten large-cap stocks that made their shareholders happy last week. The common thread? Concrete catalysts. Whether it was new contracts, partnership renewals, acquisition deals, or better-than-expected earnings, these companies gave investors tangible reasons to buy. And in a market that's constantly looking for the next winner, that's what separates the gainers from the rest of the pack.