1. A method of preparing a mouse tumor model system comprising: a) trypsinizing normal adherent F111 rat fibroblast cells; b) suspending the trypsinized F111 rat fibroblast cells on a surface coated with agarose in a medium containing Fetal Calf Serum (FCS) to obtain adhesion-deprived F111 rat fibroblast cells; c) administering subcutaneously the F111 adhesion-deprived cells to an immunocompromised mouse; and d) allowing the F111 adhesion-deprived cells to form tumors or to metastasize, or both to form tumors and to metastasize, in the immunocompromised mouse; wherein the normal adherent F111 rat fibroblast cells are non-transfected cells.