A device uses cold plasma to treat cancerous tumors. The device has a gas supply tube with a delivery end. The gas supply tube is configured to carry a gas to the delivery end. A syringe is provided having an opening. The syringe is connected to the supply tube and configured to carry the gas to the opening. A first electrode is positioned inside said syringe, and a second electrode is positioned adjacent to the opening. The first and second electrodes excite the gas to enter a cold plasma state prior to being discharged from the opening of the syringe. An endoscopic tube can be used instead of the syringe. An exhaust tube can be provided to remove gas introduced into the body cavity by the cold plasma jet.