Abstract
Many biological findings including cell death have been reported in solid tumors after radiotherapy in a fractionated regimen. 4Rs were proposed as important kinetic factors occurring after fractionated radiotherapy in the 1960s, finally leading to the discoveries such as molecular mechanisms of DSB repair, cell cycle checkpoint, hypoxia response, and identification of cancer stem cells. As for apoptosis, at first, it was believed that apoptosis only occurs to lymphatic cells, but not to solid tumor cells after irradiation; however, development of sensitive methods identified apoptosis also in solid tumors albeit with a low frequency. Furthermore, many papers reported that the frequency is well correlated with clinical results of radiotherapy. Surprisingly, the activity of caspase-3 was recently reported to contribute to the accelerated repopulation after irradiation via secretion of prostaglandin E2. In this symposium, I will review the diversity of factors which significantly affect cell death occurring within solid tumors after irradiation.
