* Merck up after US FDA approves therapy for rare lung condition

* Trump's media firm extends gains after stellar debut

* GameStop faces 'unsustainable' sales decline, shares slide

* Indexes up: Dow 0.77%, S&P 0.46%, Nasdaq 0.22%

NEW YORK, March 27 (Reuters) - The Dow was the best performing of the three major indexes on Wednesday, paced by gains in drugmaker Merck, while as investors looked towards the next piece of inflation data and Federal Reserve policymaker commentary for insight on the rate path.

Merck & Co advanced 4.77% as the biggest boost and percentage gained on the Dow after the U.S. Food and Drug Administration approved its therapy for adults suffering from a rare lung condition.

The blue-chip Dow sits roughly 1% away from breaking the 40,000 level for the first time.

Gains on the tech-heavy Nasdaq were capped by AI giant Nvidia which lost 2.59% and was on track for its second straight decline. Shares were still up more than 80% on the year, however.

Recent data that showed hotter than expected inflation in the form of consumer prices (CPI) and producer prices (PPI) failed to markedly disrupt market expectations for a rate cut of at least 25 basis points (bps) from the Federal Reserve in June.

The Fed kept its projections for three rate cuts this year intact at its policy meeting last week, which Fed officials have largely stood by this week in comments.

The Personal Consumption Expenditures Price Index (PCE), the Fed's preferred inflation gauge, is due on Good Friday, when the U.S. stock market will be closed.

"We're living in between the space of those data-heavy bookends, and the markets are largely behaving as we would expect them to in that void, which is we're seeing equities largely tread water, a little bit of weakness which I would probably chalk up more so to just quarter-end rebalancing," said Craig Fehr, head of investment strategy at Edward Jones in St. Louis.

"But we have the markets that are keenly anchored on the big data points, which is inflation, Fed decisions, and the labor market."

Later in the day, Fed Board Governor Christopher Waller is expected to speak at the Economic Club of New York later in the day.

The Dow Jones Industrial Average rose 307.35 points, or 0.77%, to 39,584.13, the S&P 500 gained 23.92 points, or 0.46%, to 5,227.50 and the Nasdaq Composite gained 35.50 points, or 0.22%, to 16,351.19.

All three major U.S. stock indexes were poised for quarterly gains, with the S&P on track for its biggest first quarter percentage gain since 2019.

Traders see a 70.4% chance the Fed will begin its easing cycle in June, according to the CME FedWatch Tool.

Nine of the 11 major S&P 500 sectors were trading higher, with rate sensitive utilities and real estate leading the best performers as bond yields eased.

Among individual stocks, Trump Media & Technology Group jumped 14.16%, a day after its stellar Nasdaq debut.

GameStop plunged 14.77% after the videogame retailer reported lower fourth-quarter revenue and said it had cut an unspecified number of jobs to reduce costs.

Advancing issues outnumbered decliners by a 3.43-to-1 ratio on the NYSE while advancing issues outnumbered decliners by about a 2.43-to-1 ratio on the Nasdaq.

The S&P 500 posted 43 new 52-week highs and no new lows while the Nasdaq recorded 131 new highs and 72 new lows. (Reporting by Chuck Mikolajczak; Editing by Aurora Ellis)