They weren't the kind of monster moves we've seen in the past from Dendreon (Nasdaq: DNDN), but shares were still volatile yesterday as a different news sent the stock in opposite directions.

On the positive side, news out of AstraZeneca (NYSE: AZN) helped the biotech. Yesterday, AstraZeneca announced that zibotentan, its potential competitor to Dendreon's prostate cancer treatment Provenge, failed one of its phase 3 trials.

Zibotentan is still in two other phase 3 trials. One is testing the drug in patients before the tumor has metastasized -- spread outside its primary location -- which shouldn't affect Provenge sales much since it's only approved for metastatic prostate cancer. The second trial is testing zibotentan in combination with sanofi-aventis' (NYSE: SNY) Taxotere, Provenge's current competitor. That trial could still be problematic for Provenge if Taxotere plus zibotentan extends survival more than Taxotere alone.

The bad news came later in the day after the Centers for Medicare & Medicaid Services (CMS) posted the questions for its Nov. 17 meeting to determine a national payment system for Provenge. The agency is questioning both its off-label and its on-label use.

Dendreon has secured reimbursement from insurers -- Aetna (NYSE: AET), Humana (NYSE: HUM), and Kaiser, in particular -- but Medicare is the mother lode considering the age of men who typically get prostate cancer. It's not a big deal if the agency restricts prescriptions for patients for which the Food and Drug Administration hasn't approved --  so called off-label use. But Dendreon needs reimbursement to include all the patients described on the label.

The evidence clearly points in the direction in Provenge working; that's why the FDA approved it, and the label is based on the clinical trials run by Dendreon. Unfortunately, the questions aren't yes-or-no answers. Instead the panel of experts are expected to rate their confidence on a scale of one to five. That leaves open the possibility of ambiguity, investors' worst enemy.

At the end of the day, after the ups and downs, Dendreon closed down just 1.3%. That's probably about right. As with its deal with GlaxoSmithKline (NYSE: GSK) last week securing a supply of a compound needed to make Provenge, investors just need to take each issue -- good or bad -- in stride. Keep an eye on the prize, Dendreon has a long and windy road until Provenge is a blockbuster.

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