Here we report that RNA interference against ATM inhibited p53 accumulation in cells expressing oncogenic STAT5 and cooperated with Rb inactivation to suppress STAT5A-induced senescence. Knocking down ATM was also effective to bypass E2F1-induced senescence and in combination with Rb inactivation, inhibited RasV12-induced senescence. Cells that senesced in response to ca-STAT5A or RasV12 accumulated DNA damage foci and activated ATM, ATR, Chk1, and Chk2, indicating that aberrant oncogene activation induces a DNA damage signaling response. Intriguingly, bypassing oncogene-induced senescence by inactivation of p53 and Rb did not eliminate the accumulation of oncogene-induced DNA damage foci (ODDI), suggesting a mechanism that may limit transformation in immortalized cells.