In this work, we have attempted to find in vivo supporting evidence for the role of ATM in p53-dependent tumor suppression and in oncogene-induced senescence using murine experimental systems, namely, Ras-induced senescence in mouse embryo fibroblasts (MEFs), Ras-induced senescence during lung tumorigenesis, and chemically-induced fibrosarcomas. Here, TP53 is linked to fibrosarcoma.