oa Editorial [Hot topic: A Dawn of New Era of Signal Transduction in Radiation Oncology (Guest Editor: Yuzuru Niibe, MD, PhD)]

Recent improvements in radiation oncology have been the most dramatic in human oncology and have yielded many fruitful outcomes in treatments for cancer patients. Improvements in physical technology have led us to a new world of treating targets from any direction using intensity-modulated radiation therapy, stereotactic body radiation therapy, and image-guided radiation therapy. Moreover, in the field of radiation biology, various important facts have been confirmed. Radiation therapy affects the chain of signal transduction within cells, between cells and outside of cells. Finally, the cancer cell dies. Hypoxia-inducible factor 1 (HIF-1α) is a biomarker of hypoxic cells [1, 2]. Harada et al., discussed the correlation between HIF-1α and radioresistance, suggesting a positive correlation between the two. In the near future, progress in molecular imaging will allow us to detect hypoxic cells and apply intensity-modulated radiation therapy combined with anti-HIF-1α molecular drugs. Proliferation of cancer cells is also very important in this field. Akimoto et al., discussed the correlation between EGFR and cancer proliferation. Overexpression of EGFR has been proven to be correlated with radioresistance. Recently, an anti-EGFR molecular targeted drug (cetuximab) combined with radiation therapy has been shown to achieve better prognosis than radiation therapy alone for head and neck cancer [3]. Angiogenesis is necessary for cancer cells to survive. Furthermore, lung injury from radiation therapy has been correlated with angiogenesis. Amano et al., reviewed angiogenesis and radiation on the basis of their group study. The effect of radiation is usually limited to the field of irradiation. However, rarely, the application of radiation shows an effect outside this field, as the so-called abscopal effect [4]. Shiraishi et al., discussed the mechanisms of abscopal effects on the basis of their studies and the literatures. Their review article suggested that radiation therapy combined with drugs inducing abscopal effects are likely to become commonplace in the near future. Oka et al., reviewed various aspects of signal transduction and radiation in brain tumors. In particular, glioblastoma was noted as the most radioresistant brain tumor, requiring exacerbation of the effects of radiation using signal transduction therpay. The combination of radiation therapy and hyperthermia is very important, and many studies have examined this issue. Ohnishi et al., discussed radiation therapy combined with hyperthermia in terms of the guardian of the genome, the p53- pathway. Heavy ion radiation therapy shows a high-LET and a sharpened dose distribution. Heavy ion radiation therapy can be lethal to radioresistant cancer cells due to the unique mode of signal transduction. However, this unique signal transduction has remained unclear. Further studies are required in the field of signal transduction. Takahashi et al., reviewed this field. Finally, a new era of signal transduction in radiation oncology is beginning.