Could we see cabozantinib (XL-184) approved some time next year?

According to a recent media release issued by Exelixis, cabozantinib (also known as XL-184) has shown effectiveness in a randomized, Phase III clinical trial in patients with advanced and metastatic medullary thyroid cancer. Obviously this is not metastatic prostate cancer, but these data look good enough for Exelixis to consider a submission for marketing approval.

Data from the randomized, Phase III EXAM trial were presented at the recent annual meeting of the American Society for Clinical Oncology (ASCO), and the slides presented at the meeting are available on the Exelixis web site.

We do not intend to go into the supporting data in detail. What is important from the point of view of men with very late stage prostate cancer is that Exelixis will probably pursue approval of cabozantinib for the treatment of advanced forms of medullary thyroid cancer based on these data. If cabozantinib is approved by the U.S. Food & Drug Administration (FDA) and/or the European Medicines Agency (EMEA), it will then be possible for medical oncologists to prescribe this drug “off label” for men with very late stage, metastatic, castration-resistant, and chemotherapy-resistant prostate cancer too.

Cabozantinib has clearly demonstrated activity in men with very late stage forms of prostate cancer, and it is currently in Phase III clinical trials (the COMET-1 and COMET-2 studies) for the treatment of men with late stages of metastatic, castration-resistant, and chemotherapy-resistant prostate cancer. How many men with advanced stages of prostate cancer will really be appropriate candidates for treatment with cabozantinib is still undetermined. However, if the product were to come available for prescription, and if the patient has exhausted all other reasonable options, and if his insurance company is willing to cover the associated costs, then it would certainly appear to offer a potentially reasonable therapeutic option on the basis of the data that are currently available (with full recognition of the fact that cabozantinib is a drug that has been associated with a significant range of possible side effects).

Assuming that the data presented at the ASCO meeting stand up to appropriate scrutiny by the FDA and EMEA, and that Exelixis can and does submit new drug applications to the relevant regulatory authorities some time in the next 6 months, then we could certainly see cabozantinib being approved for treatment of medullary thyroid cancer some time in 2013 — and possibly quite early in the year.

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