Last month, news from GlaxoSmithKline (NYSE:GSK) sent shares of Rule Breakers pick Exelixis (NASDAQ:EXEL) falling after Glaxo refused to exercise its option of Exelixis' lead compound, XL647. Yesterday, the big pharma gave Exelixis investors something to cheer about after the announcement that it was expediting its review of Exelixis' No. 2 compound, XL880.

XL880 is a targeted therapy that inhibits the VEGF and MET kinase receptors, which are often present in many different types of cancers. Exelixis has been testing the compound in phase 1 studies across various solid tumors. The company reported positive data on the drug at the American Society of Clinical Oncology medical conference in June.

As part of a collaboration agreement, GSK has the right to take over late-stage development of up to three of Exelixis' compounds. In July, Exelixis retained all rights to lead drug XL647 after GSK refused to pick it up.

If the timeline for an announcement on XL880 is similar to the decision on XL647, then word on whether GSK picks up the drug should come in about three months, following the submission of all the data to GSK in mid-September. This would mean a GSK thumbs-up (or -down) on XL880 would likely take place in December.

Other competitors, such as ArQule (NASDAQ:ARQL), also have similar compounds in development, meaning they are not far behind XL880 in the race to bring the first MET inhibitor onto the market.

GSK's request to review the data on XL880 even before it has reached the proof-of-concept milestone is undoubtedly a good sign for the drug's chances of being picked up. Unlike with XL647, GSK doesn't have any compounds similar to XL880 in its development pipeline or on the market.

Getting XL880 picked up by GSK would mean substantial milestone payments and a reduced burn rate for Exelixis now that it would no longer have to support clinical testing of the drug. Later in the year, another Exelixis compound, XL784, will also begin the review countdown with GSK, so Exelixis investors will have another two shots on goal with GSK in the coming months.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. GlaxoSmithKline is an active Income Investor pick. The Fool has a disclosure policy.