The following trial may be relevant for synovial sarcoma patients:
https://clinicaltrials.gov/ct2/show/NCT02432326
The 2 drugs have been tried separately but not on sarcoma:
http://meetinglibrary.asco.org/content/135094-144
http://meetinglibrary.asco.org/content/135128-144
The side effects were mostly gastrointestinal. They could be worse in the combination...
These drugs are so called cancer stem cell inhibitors.BBI608 is supposed to inhibit β-catenin, and Nanog pathways in particular. These pathways are active in synovial sarcoma: