This strongly suggests that the essential role of p53 in cancer suppression is dependent on Arf regulation, and that cells acquire immortality only in the presence of mutations in Arf and p53. By contrast, p53-dependent acute damage responses are even observed in cancer cells, indicating that cancer cells without p53 mutations are more sensitive to DNA damaging agents than p53-mutated cancer cells. The gene discussed is CDKN2A; the disease is cancer.