What happened Shares of the top pharmacy benefits manager (PBM) Express Scripts Holding Company (NASDAQ: ESRX) rose by 15.8% in December, according to data from S&P Global Market Intelligence. The catalyst? Investors were apparently excited about Express Scripts' $3.6 billion acquisition of the privately held medical benefits management eviCore that closed last month. Besides being immediately accretive to earnings, this deal seems to be a prelude to additional acquisitions by Express Scripts, as the company attempts to protect itself from a rapidly consolidating and increasingly competitive industry. Image source: Getty Images. So what The PBM space is set to go through a major shift in the coming years. The proposed $69 billion merger between the country's largest pharmacy, CVS Health Corporation (NYSE: CVS), and one of the largest health insurers Aetna (NYSE: AET) seems to indicate that the industry is moving toward eliminating the traditional role of PBMs as the middle-men in the prescription drug market. If true, Express Scripts, as the largest stand-alone PBM, would obviously be in a terrible position if it failed to diversify. Now what Express Scripts is undoubtedly in a tough position moving forward. While there's no telling how the CVS-Aetna merger will ultimately affect the dynamics of the PBM industry as a whole, Express Scripts must figure out a way to cut fat and deliver as much value to customers as possible in order to remain a viable operation over the long haul. Fortunately, the eviCore deal does go a long way toward eliminating inefficiencies in Express Scripts' underlying business model, and it should give the company another year or two to figure out how best to deal with this changing landscape as a result. The bottom line is that even though the fate of the PBM industry is still unclear in the wake of this game-changing merger between CVS and Aetna, Express Scripts does have the financial flexibility to adjust course as needed. This eviCore deal is clearly a much-needed first step toward that larger goal. And that's why this deeply discounted healthcare stock might turn out to be an incredible bargain for investors that are willing to let this industrywide metamorphosis play out. 10 stocks we like better than Express ScriptsWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the 10 best stocks for investors to buy right now... and Express Scripts wasn't one of them! That's right -- they think these 10 stocks are even better buys. Click here to learn about these picks! *Stock Advisor returns as of January 2, 2018George Budwell has no position in any of the stocks mentioned. The Motley Fool recommends CVS Health. The Motley Fool has a disclosure policy.