Cancer treatment using non-thermal atmospheric pressure plasma is a brand new and challenging approach for cancer therapy. Conventional cancer therapies are surgery, radio-therapy, and chemo-therapy. We propose plasma-therapy as the fourth cancer therapy. Plasma cancer therapy involves direct plasma treatment of cancers including melanomas, head and neck cancer, pancreatic cancer and liver metastasis, and indirect plasma treatment of cancers by using plasma irradiated solutions such as plasma-activated medium (PAM).We have been recently studying plasma cancer therapy using target cancers such as ovarian cancers, brain tumors, gastric cancers and skin cancers. We have developed a plasma source with ultrahigh electron density, which we have applied to these cancer cells. In addition, we found that plasma-irradiated medium itself can kill these cancer cells. This medium was termed plasma-activated medium (PAM). In vitro and in vivo studies have suggested that PAM is an important tool for cancer therapy especially for disseminated cancers that are currently untreatable.Although many dramatic therapeutic effects of plasma therapy on cancer cells have been reported, the molecular mechanisms of the anti-tumor effects of plasma remain to be elucidated. The greatest challenge for plasma medical science is to understand the complex system that mediates plasma inputs resulting in physiological outputs such as cell death of cancer cells and proliferation of normal cells. Intracellular molecular mechanisms of PAM are also being intensively studied in order to understand the mode of action of PAM. In this review, we summarize the latest understanding of plasma cancer treatments.
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