The assumption that autochthonous tumors interfere with the effector T cell (T_E) response implies that they first induce functional T cells. However, if T_E are generated, they usually remain functional, persist life-long as memory cells and prevent tumors. This holds true for some virus-induced tumors and is associated with evolutionary pressure. In contrast, models that allow monitoring of tumor antigen-specific T cells suggest that spontaneous autochthonous tumors either sneak through or induce T_E too late when the tumor has developed resistance to T_E or induce tolerance. This can be explained by the absence of evolutionary pressure.