RB1 and neoplasm: The T-cells, B-cells, and fibroblasts of these mice exhibit resistance to apoptosis and cell cycle arrest, supporting the role of SnoN as a tumor suppressor.178 Likewise, Ski tumor suppression activity has been observed in Ski-deficient mice, which exhibit higher sensitivity to tumor formation induced with carcinogens.273 Ski loss increases MEF proliferation, whereas Ski overexpression inhibits MEF proliferation via transcriptional gene repression in association with Rb and MAD.273 Both SnoN and Ski seem to be important in some cancer types.