Yesterday Amgen (Nasdaq: AMGN) presented the full data set for its clinical trial testing Xgeva's ability to delay bone metastasis in prostate cancer patients. Unfortunately, we're no closer to ending the controversy over its expanded use than we were when the top-line data was released in Dec.

Xgeva delays metastasis-free survival by 4.2 months compared to a placebo. Pushing back the time it takes for the first metastasis to occur is important because bone metastases are painful. In fact, a separate trial showed Xgeva delayed the worsening of pain in prostate cancer patients when compared to Novartis' (NYSE: NVS) Zometa.

Xgeva is already approved for use in patients with bone metastasis. If Xgeva didn't have any side effects, there wouldn't be a question of whether to use it in patients with pre-metastatic cancer -- i.e., before the use of Sanofi's (NYSE: SNY) Taxotere or Dendreon's (Nasdaq: DNDN) Provenge.

But the drug causes osteonecrosis of the jaw, the risk of which increases the longer patients are on the drug. Sure, seeing your jaw bone deteriorate isn't as bad as getting metastases, but Xgeva isn't a cure; it's only delaying the enviable.

Evidence that Xgeva delays death would help push the risk-benefit analysis strongly in favor of using it early. Unfortunately the trial wasn't set up to measure that, and it would likely require a large clinical trial to prove.

The Food and Drug Administration will get to weigh in on the risk-benefit analysis after Amgen submits a supplementary marketing application in the next month or so. I think the FDA is likely to sign off on the expanded approval, but we'll have to wait and see how doctors interpret the data.

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