What: Rumors that interest in licensing Receptos' (NASDAQ: RCPT) intriguing oral multiple sclerosis drug ozanimod have turned into interest in a full-scale acquisition drove up the company's shares by 15.3% last month.

So what: The MS market is worth $17 billion a year; according to Express Scripts, MS is the second most costly specialty indication behind inflammatory conditions such as rheumatoid arthritis.

In a bid to capture a piece of that market, Receptos is developing ozanimod, an oral MS therapy now in phase 3 trials. Because ozanimod put up impressive results in phase 2 studies, including a 53% drop in MS relapses and an arguably best-in-class safety profile, many industry watchers think it has big-time market potential.

That blockbuster thinking is supported by the fact that ozanimod is being evaluated head-to-head against one of the globe's best-selling MS therapies, Biogen's Avonex. Avonex has long been the linchpin in Biogen's MS drug franchise, with sales totaling $3 billion last year even though the drug has been on the market since 1996.

However, the MS market is ripe for Avonex successors.

Because Avonex is injected rather than taken as a pill, its dosing isn't ideal. Also, although Avonex works for many patients, recently launched oral therapies might be more effective. Novartis' Gilenya, for example, outperformed Avonex in its trials, and its sales have surged since its launch, reaching $638 million in the first quarter.

With next-generation MS therapies primed to grab market share, it's probably not surprising that there's lots of speculation about Receptos as a possible buyout candidate.

Now what: There's no guarantee that a suitor will acquire Receptos, but the company's management has previously indicated willingness to -- at a minimum -- team up with a partner on ozanimod to reduce its expenses.

Licensing deals are common across biotech and normally include up-front cash, the potential for regulatory and sales milestones, and royalties tied to sales if the drug is approved.

Such a licensing deal might be the more likely outcome for Receptos than an acquisition. However, given that the MS market is attractive, and that ozanimod could work better than Avonex and offer placebo-like safety, I wouldn't be shocked by a deal, either.

Regardless, Receptos is clearly one to watch.