When the Food and Drug Administration advisory panel meets tomorrow to review expanding the approved indication for Amgen's (NAS: AMGN) Xgeva, the committee of outside experts will have two main issues to debate: Is bone-metastasis-free survival -- the primary endpoint in the trial -- a reasonable measurement of benefit? And do the benefits outweigh the side effects?
The answer to the first should be a resounding "Yes." The second is a little more up for debate.
Amgen is trying to expand the label of Xgeva to be used before prostate cancer has spread to the bone. It's currently only approved to help prevent bone breaks in patients who are already so advanced that the cancer has spread there.
Xgeva extended the time it took the tumor to start growing outside of the prostate -- to metastasize -- on the bone by 4.2 months. The endpoint is actually bone-metastasis-free survival, which includes not only time for bone metastasis, but also death if that would come first, which helps capture any severe toxicity the drug might have.
Neither metastasis-free survival nor progression-free survival (the latter of which just measures whether the tumor starts growing again, plus the same "death by drug" issue) is as good as overall survival; the ultimate goal is obviously to have patients live longer. But metastasis-free survival is more clinically relevant because metastases are painful and can lead to bone breakage.
If the committee doesn't buy that argument, it may be bad news for Exelixis (NAS: EXEL) , which is running a trial measuring their drug cabozantinib's ability to reduce pain in patients with prostate-cancer metastases.
The harder question to answer is whether a 4.2-month delay in the tumor spreading to the bone justifies the side effects that Xgeva causes. In the clinical trials, 5% of patients developed osteonecrosis of the jaw -- essentially, death of the jaw bone -- which can be painful in itself. There's also worry that Xgeva inhibition of bone metastases in particular might just shift their formation to other parts of the body. Amgen has an uphill climb tomorrow to convince the oncologists on the panel to recommend approval of the drug.
While investors in other prostate-cancer drugs will be watching tomorrow's meeting, I don't think a surprise recommendation for approval would really be that bad for Johnson & Johnson's (NYS: JNJ) Zytiga or Dendreon's (NAS: DNDN) Provenge, since both are used after a tumor has metastasized. Same goes for Medivation's (NAS: MDVN) MDV3100, which isn't approved yet, but likely will be. Even if Xgeva is approved for use before these drugs, they'll only have to wait 4.2 months to get their hands on the patients.
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