RB1 and liver cancer: This deleterious missense mutation inhibits tetramer formation and lacks transcriptional activity but is infrequently mutated in human tumors being reported in only a rare liver cancer in the International Agency for Research on Cancer TP53 database.26, 27 Taken together, these data demonstrate that p16 suppresses immortalization of RB1-deficient lung epithelial progenitor cells, and that epithelial immortalization after p16 loss does not require loss of p19Arf or Trp53.