I just found this old article (2009) about the frequent methylation of RASSF1A in synovial sarcoma and the anti-tumor effects of 5-aza-2'-deoxycytidine against synovial sarcoma cell lines:
http://www.springerlink.com/content/h1125350187h0408/
There are open trials for the drug decitabine but only for other types of cancer (mostly AML) :-(