cocarcinogen
(ˌkəʊkɑːˈsɪnədʒən; ˌkəʊˈkɑːsɪnəˌdʒɛn) na substance that can promote cancer when acting with other substances, but which does not promote cancer by itself
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014