A new study looked at the expression of the proteins associated with epithelial-mesenchymal transition in synovial sarcoma and concluded that monophasic synovial sarcoma may have developed through epithelial-mesenchymal transition:
http://www.ncbi.nlm.nih.gov/pubmed/21809991
To understand what epithelial-mesenchymal transition means:
http://en.wikipedia.org/wiki/Epithelial-mesenchymal_transition