It has been a rough couple of weeks for Rule Breakers pick Exelixis (Nasdaq: EXEL). Its shares have fallen to levels not seen since 2003 as investors lose interest in development-stage drugmakers. As one Rule Breakers member asked, with shares of Exelixis so low, wouldn't it make a great acquisition target for big pharma companies looking to stock their pipelines?

It's hard to argue that Exelixis, with its large pipeline, wouldn't be a tasty acquisition. Some large-cap pharmas like AstraZeneca (NYSE: AZN) definitely need to sign some deals to make up for blockbuster drugs that will lose patent protection, and we've seen some interesting deals in recent weeks (here and here, for example).

Now is as good a time as any for the big companies to make deals, because they're cutting their research and development budgets to bolster earnings and are still flush with cash, like the more than $13 billion sitting on Novartis' (NYSE: NVS) balance sheet. While it sometimes seems like anything is possible in this crazy sector, there are a couple of reasons why Exelixis probably isn't going to be acquired anytime soon -- or at all.

The biggest impediment is the fact that a majority of its compounds are already outlicensed to or subject to development agreements with partners such as GlaxoSmithKline (NYSE: GSK), Genentech (NYSE: DNA), and Bristol-Myers Squibb (NYSE: BMY). These partnership deals not only complicate any acquisition because of change-of-control agreements (just look at what happened to Biogen Idec (Nasdaq: BIIB) last year), but also dampen the rewards from acquiring Exelixis.

The second issue is also what makes Exelixis so attractive right now -- its cheap price. Ignoring its long-term and convertible debt, Exelixis is only trading at a market capitalization just above $600 million and has about $150 million worth of working capital on its balance sheet. Exelixis also has multiple pipeline compounds entering mid- and late-stage development this year, so management is probably not going to want to sell out after all these years of working to get to this point.

The prospect of a large acquirer paying a premium price to acquire Exelixis is not an implausible thought, nor is it usually worth buying shares of a biotech on the hopes of a buyout. Regardless, for the above reasons, a buyout probably won't be in the works anytime soon, and we'll likely see Exelixis stay independent for a while (at least), even though it will need to raise more cash in about year.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. GlaxoSmithKline is an Income Investor pick and Biogen is a Stock Advisor recommendation. The Fool's disclosure policy won't be bought out.