On Monday's conference call, Exelixis CEO Morrissey said initial feedback received from FDA in August suggested the agency was willing to grant an SPA for the pain relief trial. However, the FDA changed its tune in follow-up comments sent to the company in October. Patients enrolled in the cabozantinib studies will have advanced, metastatic prostate cancer that no longer responds to the standard chemo regimen of Taxotere and J&J's Zytiga. These are very sick prostate cancer patients with significant prostate cancer-related pain who have few or no treatment options left. The first study with a pain relief endpoint will begin before the end of the year. The second study, with an overall survival endpoint, will begin in the first half of next year. --Written by Adam Feuerstein in Boston. >To contact the writer of this article, click here: Adam Feuerstein. >To follow the writer on Twitter, go to http://twitter.com/adamfeuerstein. >To submit a news tip, send an email to: email@example.com. Follow TheStreet on Twitter and become a fan on Facebook.