I'm a little surprised that Exelixis' (NASDAQ:EXEL) cancer drug cabozantinib hasn't gained Food and Drug Administration approval yet, which worries me a little.

But just a little.

Sure, the FDA set Thursday as its goal for approving the drug. It has every right to wait until then to make a decision. And the date with destiny is only a goal; the Prescription Drug User Fee Act, or PDUFA, that designates the date gives the FDA the leeway to make a decision anytime before or after the PDUFA date.

Recently, the FDA has been making decisions well ahead of the date. PDUFA dates for Pfizer's (NYSE:PFE) Xeljanz and Medivation's (NASDAQ:MDVN) Xtandi were last week, but both were approved awhile ago -- Xeljanz at the beginning of the month and Xtandi way back in September. The Office of Hematology and Oncology Products has been especially prolific, having approved Bayer and Onyx Pharmaceuticals' (NASDAQ: ONXX) Stivarga, a month ahead of its PDUFA date.

After the FDA canceled the advisory committee meeting back in August, I kind of figured that the FDA was close to approving the drug; there's no reason to get the opinion of outside experts if everyone at the agency already agrees the drug should be approved.

But after we blew through September and October and we didn't get a push-it-out-before-the-holiday approval last week, investors should be getting a little worried.

The efficacy data on cabozantinib in medullary thyroid cancer are pretty solid. And it's a drug for terminal cancer, so any side effects aren't likely to be a major issue.

That leaves manufacturing as the most likely area that could be tripping up the drug. This will be Exelixis' first drug, which could be a worry. Or maybe not; plenty of companies have gained FDA approval for their first drug without a hitch. Manufacturing is a black box for investors, so there's no way to know.

If cabozantinib is rejected for some minor reason, it won't be the end of the world. Medullary thyroid cancer isn't going to make cabozantinib a blockbuster. Sales will help the company slow the cash burn, but to get to profitability, Exelixis has to get the drug approved for one of the larger cancer indications. Cabozantinib is being tested in prostate, breast, and lung cancer.

As long as Exelixis can clear up any issues before those indications are ready for review, the decision this Thursday -- if it comes then -- won't really matter for the long-term future of cabozantinib and Exelixis.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.