If you go to clinicaltrialsdotgov and use "cabozantinib" as your search query...which is what I do.
You will find a 44th trial has been added - Ponatinib in Advanced MTC.
An NCI-sponsored P2 that mentions both Cabo & Vandetanib as comparators.
Not yet recruiting. It does pay to watch what all the competition is doing.
MTC is a RET driven cancer and Ponatinib has an even lower IC50 number for RET than Cabo; the rationale is there but the market is small and there might be confounding factors other than RET as well.
It's also interesting that the circumstances behind the birth of the two drugs is so different: Ponatinib was designed from the ground up with a warhead like protrusion in its molecular structure for better receptor inhibition whereas Cabo was found through systematically testing thousands of random compounds.