Molecular mechanisms involved in tumor repopulation after radiotherapy.

Radiotherapy remains one of most important treatment modalities for solid tumors. Current radiotherapy is mostly based on a set of concepts called the 4"R"s, which were established when there was lack of understanding of the underlying molecular mechanisms. However, progress made in the past two decades are beginning to allow us to see some of the molecular details involved in tumor response to radiation therapy. In this review, we will attempt to summarize some of the key discoveries in molecular radiation biology that have direct relevance to radiotherapy. We will focus our discussion on areas such as radiation induced tumor vasculogenesis, stem cell mobilization, and cellular repopulation. We hope our discussion will stimulate further studies in this important area of cancer research.