The S&P 500 may have ended March with a negative return of 1.7%, but not every stock from the famous index had a down month. In fact, a handful of stocks -- Micron Technology (NASDAQ:MU), FMC Corporation (NYSE:FMC), and Vertex Pharmaceuticals (NASDAQ:VRTX) -- were able to post double-digits gains during the period. Here's why.

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A stellar earnings report

Micron Technology -- a memory chip manufacturer -- posted a 17.7% gain in March on the back of a terrific fiscal second-quarter earnings release. The company's DRAM and NAND chips are benefiting from tight supply and strong demand, which is leading to increasing pricing. The combination allowed the quarterly top line to grow by 58% year over year. What's more, Micron also made progress at bringing down its manufacturing costs, allowing non-GAAP gross margin to nearly double to 38.5%. Surging revenue and expanded margins allowed Micron to post more than $1 billion in earnings for the period. That's a huge uptick compared to the $12 million profit recorded in the year-ago period.

The blowout earnings report allowed management to raise its guidance for the full year, too. The company now projects that fiscal 2017 revenue will be $4.65 billion, and non-GAAP EPS will be $0.86, both of which compare favorably to its prior outlook and Wall Street's expectations. Management credited the bullish forecast to cost improvements, higher pricing, and favorable mix shifts.

Micron's business is on fire right now, so it isn't hard to figure out why shareholders enjoyed yet another period of gains.

The market applauds an asset swap

Shareholders of the chemical company FMC Corporation were treated to a 17.5% jump in March after news broke that it was trading its own health and nutrition division for a "significant portion" of DuPont's (NYSE:DD) crop protection business. As part of the deal, FMC Corp also agreed to make a $1.2 billion payment to DuPont.

DuPont agreed to this deal in an effort to appease European regulators so that it could move forward with its proposed merger with Dow Chemical. Regulators have been hesitant to sign off on this mega-merger, but this asset divestiture to FMC should help to alleviate antitrust concerns.

Wall Street appears to love this deal since it will turn FMC Corp into the fifth-largest crop protection specialist in the world. In addition, this deal is expected to add $1.5 billion in revenue and $475 million in EBITDA to FMC's financial statements this year. Finally, this asset swap will significantly enhance FMC's research and development capabilities and beef up its pipeline, so it looks like a true home run for long-term shareholders.

Upbeat clinical data sends this biotech stock higher

Investors in biotech giant Vertex Pharmaceuticals enjoyed a 19% pop in March thanks to positive results from Vertex's phase 3 EVOLVE and EXPAND studies. These trials were designed to evaluate the efficacy and safety of an experimental cystic fibrosis (CF) drug called tezacaftor in combination with the company's FDA-approved CF drug ivacaftor, which is marketed under the brand name Kalydeco. 

The results from the EVOLVE study showed that patients who used the tezacaftor/ivacaftor compound demonstrated a statistically significant improvement when compared to patients who only received a placebo. Better yet, the combination therapy was well tolerated by patients and led to lower rates of serious adverse events when compared to the placebo.

The data from the smaller EXPAND study was just as encouraging. Patients who used the tezacaftor/ivacaftor combination drug also showed a statistically significant improvement when compared to placebo and ivacaftor as a monotherapy. 

Management said the data from both studies was strong enough to justify regulatory submission. If all goes well, this new combination therapy promises to grow Vertex's addressable market by 75%, and it could help the company remain one step ahead of potential competitors.

Given the wonderful news, it is easy to understand why investors felt that Vertex deserved a higher valuation. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.