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Everybody likes highfliers, and there's a lot of talk about the biggest year-to-date gainers now that we're approaching the end of another quarter.

Naturally, Apple (AAPL) and other large caps spring to mind. But the reality is that smaller companies have a heck of a lot more room to run, by virtue of their upside potential.

After all, how much bigger can a company like Apple get? It might keep growing, but does anyone expect this stock to double? How about triple? Or better yet, race up more than 600%?

Yet that's the kind of performance we've seen in some of the hottest small-cap stocks on Wall Street this year.

I ran through the top performers of the Russell 2000 Index ($RUT.X) -- the most popular small-cap benchmark -- to exclude the microcaps, focusing instead on small and midsized businesses that have seen exponential growth in the year's first nine months.

Returns on the top 10 stocks on my list range from 210% to 670% returns since Jan. 1. Here's a closer look:

No. 10: Bon-Ton Stores

Stock symbol: BONT
YTD gain: 210%

Shares of Bon-Ton Stores have soared thanks to several factors, but profits aren't among them.

The department store chain is severely pressured by the macro picture, as are many other brick-and-mortar retailers, such as Abercrombie & Fitch (ANF) and J.C. Penney (JCP), thanks to weak spending and the rise of e-commerce rivals like (AMZN).

However, a new chief executive taking over early this year sparked a rally (and a short squeeze, it seems). A recent rating upgrade to "buy" from "hold" from KeyBanc Capital Markets helped sustain the rally.

No. 9: Xoma

Stock symbol: XOMA
YTD gain: 235%

Xoma is a beginning-phase medical company that develops antibody-based therapeutics. It's bleeding cash as it works toward clinical trials and (hopefully) eventual approval of its treatments, which could produce profits and possibly be followed by a buyout offer from Big Pharma.

Xoma has soared on a favorable outlook for its drug Gevokizumab, which was granted "orphan drug" status by the U.S. Food and Drug Administration for a condition known as uveitis, a swelling or inflammation of the middle layer of the eye.

If all goes well, Xoma could be taking the fast track to a wide-open market with this treatment.

No 8: Orexigen Therapeutics

Stock symbol: OREX
YTD gain: 255%

Orexigen Therapeutics peaked at $7.73 in July before dropping off sharply, but the stock came fighting back on the hopes that the company's obesity drugs will be well received. The reason isn't anything particularly extraordinary on the Orexigen front, but simply a sympathy bounce, thanks to enthusiasm over other obesity drugs.

The FDA's advisory panel has ruled favorably on Arena Pharmaceuticals' (ARNA) drug Lorcaserin and Vivus' (VVUS) medication Qnexa, and these rulings could pave the way for other treatments.

Orexigen Therapeutics is hemorrhaging cash as it works on its research but, given the nation's obesity epidemic, the company is situated in a very good place in the medical industry.

No. 7: Patrick Industries

Stock symbol: PATK
YTD gain: 255%

Patrick Industries is a distributor of building products and materials that are used in the mobile-home and recreational-vehicle industry. Bullishness on housing has buoyed the stock in 2012.

In its fiscal second quarter, the company posted per-share earnings of $1.22, more than its earnings in the preceding two fiscal years combined. And when you consider that Patrick Industries lost money in both 2008 and 2009, you can understand why investors are interested in the company as a turnaround story.

No. 6: Pharmacyclics

Stock symbol: PCYC
YTD gain: 325%

Pharmacyclics is a clinical-stage biotech focused on treatments for cancer and immune-system diseases.

Pharmacyclics also is bleeding cash, as it's focused now on clinical trials instead of marketing and sales. But favorable outlooks for its leukemia, lymphoma and autoimmune drugs appear to be buoying the valuation in anticipation of future sales.

The important thing to remember with all this and other biotechs is that they are highly speculative, and the lion's share of gains can come quickly, on even one favorable FDA report. Conversely, all it takes is a bad clinical result to ruin the company.

So know the risks before you dabble in this sector.

No. 5: Arena Pharmaceuticals

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Stock symbol: ARNA
YTD gain: 350%

Earlier this year, Arena Pharmaceuticals' Lorcaserin became the first new prescription weight-loss drug to win FDA final approval in more than a decade, tapping into a highly lucrative market.

Of course, Arena does other things, too. This clinical-stage biopharmaceutical company is also dabbling in treatments for cardiovascular, neurological, inflammatory and metabolic disorders.

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