Were any of the prior chemotherapies initially active?
This looks like a relatively safe compound that could potentially make a previously active chemo active again:
http://www.cancerresearchuk.org/cancer-info/news/archive/cancernews/2013-10-02-Blood-pressure-drug-improves-effect-of-chemotherapy-in-mice?view=n-and-r-homepage
Here is the research article:
http://www.nature.com/ncomms/2013/131001/ncomms3516/full/ncomms3516.html
There is also a trial ongoing with this compound, although I think it is in combo with radiation.
Hopefully someone from the Cabozantinib trial will post a response to your question. Trial results, even partial results, would be so helpful to hear.
Take care,
Jason