Image source: Flickr via user Heinrich-Böll-Stiftung.

Although controversial billionaire George Soros vowed to step down from managing the Soros Fund Management in full last year, his firm remains a top name in the eyes of Wall Street because of its keen ability to outperform the broader markets on a regular basis. 

Interestingly, the recently released 13F filing shows that the Soros Fund Management didn't have much of an appetite for stocks in the volatile healthcare sector in the fourth quarter of 2015. However, the firm did open a new, albeit small, position in Opko Health (OPK -1.60%) -- reportedly buying 55,500 shares during the three-month period. 

With this in mind, let's consider if this speculative healthcare stock might also be a good pick for retail investors going forward. 

Opko Health could have a transformative 2016
The big picture is that Opko Health is a diversified biopharma and diagnostics company that is closing in on two pivotal value drivers -- namely, the improving reimbursement status with payers for its 4Kscore prostate cancer test, and the forthcoming regulatory decision from the FDA for its experimental drug, Rayaldee, indicated for secondary hyperparathyroidism in patients with chronic kidney disease (CKD). 

According to a recent investor presentation, Opko is confident that it can dramatically amp up coverage for 4Kscore this year because the test has the potential to reduce costs stemming from unnecessary MRIs and prostate biopsies by 40% to 55%. 

Turning to Rayaldee, this oral vitamin D prohormone drug is facing a target PDUFA date with the FDA of March 29, 2016, meaning that, if approved, it could be on the market by as early as the third quarter of this year. Investors are excited about this particular drug candidate because it would be launched into a market that's already valued at over $12 billion a year. Moreover, the CKD market as a whole is expected to keep growing at a respectable CAGR of 1.21% over the next three years.

The good news is that Rayaldee met all of its primary efficacy and safety endpoints in late-stage testing, and thus appears to be a superior therapeutic option compared to potential competitors such as Amgen's blockbuster drug Sensipar.

Perhaps the most tantalizing part of the Rayaldee story, though, is that Amgen reported that Senispar's sales increased 21% in the fourth quarter of 2015 due to increases in both the drug's unit price and rising demand -- showing the outstanding commercial potential for drugs indicated for secondary hyperparathyroidism in general. 

The bottom line is that Wall Street thinks that the combination of rising 4Kscore test sales and the commercial launch of Rayaldee could drive the company's annual revenue up by 157% to $1.3 billion this year, making it one of the fastest-growing mid-cap healthcare stocks at the moment. 

Is Opko a compelling buy right now?
There's a lot to like about this mid-cap healthcare stock's strong growth prospects moving forward. However, there's no such thing as a sure bet when it comes to the FDA and regulatory decisions. That's why I'd recommend holding off from following in the Soros Fund's footsteps on this stock until the Rayaldee regulatory decision comes to pass. If this drug is approved after all, there should be significant upside potential remaining, with far less risk.