Biotech stocks are among the market's riskiest, but investors willing to accept the potential for pipeline failure might consider owning these five small-cap biotech stocks in 2015. All five have intriguing therapies in late-stage clinical trials, and three have high-profile big-cap partners.

Source: Flickr user Carlos Gracia

1. Proven performer 
Insys Therapeutics
(NASDAQ:INSY) is already rewarding shareholders with rapid sales growth and profitability, but investors could also benefit from a slate of late-stage research programs.

Sales of Insys' Subsys, an opiate used to treat breakthrough cancer pain, climbed 105% to $58.2 million in the third quarter, and that sales run rate of $234 million has analysts thinking the company could earn $1.67 per share next year. Insys, also plans this quarter to file for approval of its oral drug dronabinol, a unique formulation of the marijuana-based drug marinol. If approved, oral dronabinol could capture a big chunk of the marinol market, which Insys estimates is worth $150 million and is growing 4% annually. Additionally, Insys' plans include having five phase 3 research trials under way by the end of 2015, including trials evaluating its synthetic marijuana cannabinoid CBD as a treatment for epilepsy patients.

2. Revolutionizing a major indication
Investors focused on hepatitis C drugmakers last year for good reason. Three million people in the United States and another 9 million in Europe suffer from the disease, which has next-generation therapies from Gilead Sciences racking up billions of dollars in sales. The commercial success of these new hepatitis C drugs might mean that Achillion Pharmaceuticals (NASDAQ:ACHN) captures more attention this year given that its drug ACH-3102, when dosed along Gilead's Sovaldi, has been shown to deliver 100% cure rates in as little as six weeks. That could suggest that Achillion, which is developing an in-house alternative to Sovaldi to use in its combination therapy, could someday help reduce treatment regimens from their current eight and 12 weeks.

3. Leveraging Big Pharma's wallet
For decades, warfarin was doctors' go-to anticoagulant for treating heart disease and post-operative patients. However, doctors are increasingly embracing next-generation therapies known as Factor Xa inhibitors. Those Factor Xa drugs, which include Johnson & Johnson's Xarelto -- a $1 billion a year blockbuster -- reduce monitoring and brain hemorrhage risk, but they have one significant drawback: they lack a reversal agent. That means there are limited options available to doctors for Factor Xa patients who suffer a bleeding event or require emergency surgery.

As a result, J&J and its Factor Xa peers have been helping finance Portola Pharmaceuticals(NASDAQ:PTLA) andexanet alfa, a novel drug that has already proven effective in reversing Factor Xa therapies, including Xarelto, in phase 3 studies.

Despite big pharmaceutical companies helping finance this research, Portola has held on to andexanet alfa's commercialization rights, which suggests that if the drug eventually wins regulatory approval, the company could benefit handsomely. Additionally, Portola is developing its own Factor Xa drug, which is also in phase 3 trials and could one day compete with J&J for Factor Xa market share.

Source: Flickr user GoRun26

4. Improving treatment options
Curing age-related and diabetes-related vision loss has proven lucrative for
Novartis, which markets Lucentis, and Regeneron, which markets Eylea. Both Lucentis and Eylea are multibillion-dollar a year therapies, and that might suggest Ophthotech (NASDAQ:ISEE) could have a top-selling drug on its hands soon, too.

Ophthotech is developing Fovista as an adjunct therapy to be used alongside Lucentis and Eylea to boost their effectiveness. So far, trial results have been encouraging. As a result, Novartis inked a deal last year to get its hands on international rights to Fovista, agreeing to pay Ophthotech $200 million up front, as much as another $800 million in milestones, and royalties on any future foreign sales. Ophthotech retains the U.S. rights to Fovista, so an eventual approval for use alongside these two big sellers could mean the company's $1.7 billion market cap is too low.

5. A vested interest
Acceleron Pharma
 (NASDAQ:XLRN) is working on four internally discovered therapies for cancer and rare diseases, and all four are expected to be in either phase 2 or phase 3 trials by year's end.

Of the four, sotatercept is one of the most intriguing, thanks to Acceleron's partnership with biotechnology powerhouse Celgene on the drug. Sotatercept is being studied as a treatment for rare blood disorders and cancers, including multiple myeloma, an indication that accounts for the lion's share of Celgene's revenue. Sotatercept is expected to enter phase 3 trials this year; if successful, Celgene is perfectly positioned to turn this drug into a top seller. Importantly, Celgene isn't just Acceleron's development partner; it is also a major investor that owns a 14% equity stake in the company. No one knows if that means Acceleron could one day become an acquisition target for its partner, but Celgene's confidence in Acceleron's potential is certainly another reason to consider owning it.

Looking ahead
Biotechnology investing carries more than its fair share of risk. Historically, 90% or more of drugs that enter clinical trials never make it past regulators to market. As a result, any number of things could derail these promising small-cap companies. However, all five of these companies have intriguing programs that are heading down the final stretch, and that could make them worth the attention of risk-tolerant investors this year.