EMT describe cells' change in their state from being epithelial to the mesenchymal class. So, if a cancer cell line is gaining properties that allow it to move, it might reach the metastasis phase, were a cell can move to any point of the body and start a new tumor there. As in the wikipedia page you linked:
EMT has also been shown to occur in wound healing, in organ fibrosis and in the initiation of metastasis in cancer progression.
I am not aware of any kind of database for the EMT process, the most relevant resource might be the gene ontology, which has a term for it, which lists 185 (human) genes as related to this biological process.
ArrayExpress is a database of transcriptomics, it :
stores data from high-throughput functional genomics experiments
You can evaluate the role of EMT in the data stored in the database.