In Cancer Gene Census (CGC) dataset, (cgc link, there is a column named Role in cancer. The values of this attributes are 'fusion', 'oncogene', 'oncogene, fusion', 'oncogene, TSG', 'TSG, fusion', 'oncogene, TSG'. What does the 'fusion' mean? Does this mean a mixture? Or a gene that sometimes acts as OG and sometimes as TSG?