The following article suggests that a majority of synovial sarcoma tumors express PD-L1 and the expression is associated with a poorer outcome:
http://annonc.oxfordjournals.org/content/25/suppl_4/iv503.4.abstract?ct=ct
There are a bunch of anti-PD-L1 therapies in clinical trials right now:
http://clinicaltrials.gov/ct2/show/NCT01772004
http://clinicaltrials.gov/ct2/show/NCT01975831
http://www.clinicaltrials.gov/ct2/show/NCT01375842