Although the reason for the increase in the expression of Pai1 and Plau genes in C90 tumors must be cautiously assessed in further studies since the Pai1 and Plau proteins are correlated with metastatic potential of cancer cells40,41, treatment outcome of radiotherapy42, and poor prognosis of cancer patients43,44, our results also mean that C-ion irradiation might be superior to photon irradiation in regard to preventing acquisition of tumor aggressiveness. This evidence concerns the gene SERPINE1 and cancer.