A new approach for cancer treatment is based on the congenital overproduction of hydroxyl radicals (OH) and hydrogen peroxide (H₂O₂) in cancer cells. Recently, atmospheric pressure non-thermal plasma jet (APPJ) have been frequently used for cancer treatment through the generation of different kinds of ROS species. However, APPJ still has some demerits, such as durability after treatment. Hence, in this work, H₂O vapour is applied as a synergetic agent to APPJ, which not only controls the temperature rise, but also enhances selectivity by increasing the level of H₂O₂ and OH radicals during treatment. We observed that due to the increased concentration of OH radicals, apoptosis was induced on SK-BR3 breast cancer cells through an enhancement of oxidative signalling, which inhibits the phosphorylation of extracellular signal-regulated kinases (Erks) and activates the phosphorylation of mintogen-activated protein kinases (p38-MAPK). Furthermore, we studied the DNA damage, and PARP-1 cleaved analysis from treated cancer cells. The results show that OH/H₂O₂ plays a pivotal role in not only inducing cell death but also in enhancing the selective killing effect.