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Since the failure of Pfizer's (PFE) $160 billion megadeal to buy Allergan and move its headquarters, on paper, to lower-tax Ireland, shares of the pharmaceutical giant have been moving upward. In fact, the stock is up around 12% since early April, when the likelihood of the merger being called off became apparent.

More recently, Pfizer has announced some eye-popping deals to boost profits and sales quickly, including the $14 billion buyout of cancer biotech Medivation (MDVN) and its blockbuster prostate cancer drug Xtandi. While I'm optimistic about Pfizer's future, the company needs to play its cards carefully in the next few quarters because big risks are lurking under the surface. In particular, here are three wild cards that could propel the big pharma's shares sharply downward in the next few months.

The first wild card: Management scuttles the idea of a company split

The idea of Pfizer splitting into two entities is front and center on shareholders' minds this year, with management saying a definitive decision should come by the end of 2016.

Advocates of a split believe it would unlock significant shareholder value trapped in Pfizer's conglomerate structure. In particular, top revenue-generating assets, such as Ibrance, Enbrel, Lyrica, Eliquis, and Xeljanz, could be unchained from Pfizer's slower-moving product lines.

Since Pfizer's top-line growth has been sagging, in part due to the difficulty of meaningfully growing revenues once a company exceeds $50 billion a year in revenue, it seems likely the market will punish the stock if the split doesn't happen. Add to that the fact the split is expected, with many analysts citing Pfizer's $17 billion deal to buy intravenous-drug maker Hospira, as well as the recent Medivation deal, being all about juicing up its divisions in preparation for a split.

Pfizer has fended off years of relentless pressure from analysts and others to break up. In addition, the new acquisitions could just as easily indicate that management has now found ways to accelerate growth and profit without a split. That being said, I don't personally think it's likely the split will be called off -- but it's still a risk.

The joker in the deck: Pipeline failures

Pfizer's pipeline is one of the largest in the world, with over 90 drugs in clinical trials or beyond trials and registered with the FDA for approval. Of those, nine drugs are in the headline-generating registration phase. Given so many shots on goal, it's not just possible, but probable, that one or more drugs disappoint.

One drug that could either shoot to stardom or flame out is avelumab. The oncology drug, co-developed with Merck & Co. (MRK 0.34%), could be filed with the FDA as soon as the second half of 2016. Pfizer rates it as a significant pipeline opportunity, with estimated peak sales at $1.9 billion. With the expectations behind this drug, it needs to stay on its timeline.

And then there's Ibrance, Pfizer's breast cancer-treating superstar. The drug is up for EU evaluation by the end of this year. Since this drug has immense potential, anything but a full-on approval would likely hurt Pfizer's stock.

Also up for approval is a med from Pfizer's $5.5 billion deal to buy California-based Anacor Pharmaceuticals. The topical gel crisaborole, for eczema treatment, is currently under FDA review. Pfizer believes crisaborole could reach or exceed annual sales of $2 billion. A regulatory decision is expected by January 2017.

The ace of spades: The acquisition spree doesn't pay off

M&A deals are not a prescription that always works in a shareholder's favor. While Medivation fits well with Pfizer's bid to conquer cancer, pricing power in this therapy area could be winding down. While cancer drug prices have held up thus far, things could erode rapidly if the federal government goes beyond taking potshots at high-priced drugs and starts playing hardball.

In addition, the current market frenzy around oncology assets is leading to acquirers paying top dollar. Indeed, all the jockeying with other drugmakers led to the Medivation deal costing Pfizer more than 14 times Medivation's revenue guidance for 2016.

Medivation's lead drug, Xtandi, had $2.2 billion in revenue in the last four quarters, and it is projected to reach $4 billion in five years. But it may fall well short, since Xtandi faces competition from Johnson and Johnson's Zytiga. Worse, Medivation's two clinical-stage oncology assets, PARP inhibitor talazoparib and antibody pidilizumab, share the risk of any investigational drug -- they still have to run the FDA gauntlet.

Always play cards close to chest, because no safe stocks exist

Big pharma companies are often regarded as safe stocks, but that's an illusion. They can still present big risks for investors: Drugs in development often don't work, drugs fail in clinical trials, and the FDA can drop the ax. Even if drugs are approved, their addressable market can be snared by a competitor, or they may become targets for cost-conscious regulators.

Let's not end on a gloomy note, because Pfizer looks to be on a good trajectory right now. In particular, Ibrance is a fantastic cornerstone to a growing cancer franchise, and the drugmaker's rising price in a listless market looks promising. But there's always the chance of a messy surprise coming, so keep your powder dry.