Adverse effects of cardiopulmonary bypass on cancer prognosis are expected but have not been confirmed. Seventy-four cancer patients who underwent cardiac surgery before cancer therapy were followed up for 42 ± 37 months; 45 had cardiac surgery with cardiopulmonary bypass. There was no significant difference in cancer recurrence (40.0%) and deaths (26.7%) among patients who had cardiopulmonary bypass and those who underwent off-pump cardiac surgery (27.6% and 24.1%). There were no significant differences in freedom from cancer-related death at 2 and 5 years after cardiac surgery (78.4% and 68.5%) in the cardiopulmonary bypass group compared to the 29 off-pump group (81.8% and 58.3%). Despite some limitations, this study detected no significant adverse effects of cardiopulmonary bypass on cancer prognosis. Although these results do not verify the safety of cardiopulmonary bypass from an oncologic aspect, they suggest it can be applied in cancer patients who require cardiac surgery.