The present invention relates to methods of identifying the susceptibility of cells to reovirus infection by measuring constituive ras-MAP signaling. The invention also pertains to methods using reovirus for the treatment of cellular proliferative disorders, and particularly cellular proliferative disorders wherein the proliferating cells exhibit constitutive MAPK phosphorylation, in mammals. In particular, the methods provide for reovirus treatment of mammals to treat proliferative disorders which include breast tumors, a subset of tumors in which mutation of the ras gene is not believed to play a significant role.
