腫瘤細胞周圍的外在環境會影響放射反應的成效，而在腫瘤微環境中的內皮細胞和免疫浸潤細胞則是顯著影響放射治療結果的兩個關鍵因子之一。在分次放療中，會引發 HIF-1 和 VEGF 的增加，因而降低分次放療的優勢。另外，抗血管新生藥物的療效會被腫瘤微環境中的內生性血管生成前趨細胞所中和。除了血管之外，淋巴細胞也在腫瘤微環境中扮演很重要的角色。免疫細胞的組成種類不同，對於放射治療的效果也有很大的影響。在這篇文章中，我們探討了最近一些針對腫瘤微環境中免疫細胞重要性的文獻。目前正在發展中的合併放射治療以及免疫治療或其他調控整個腫瘤微環境的方式，有可能在不久的將來會有豐碩的成果。

Radioresponse is influenced by factors extrinsic to cancer cells.
Endothelial cells and infiltrating immune cells within the tumour microenvironment are the two components that significantly affect
the outcome of radiotherapy. The benefits of fractionated radiotherapy are reduced by up-regulation of hypoxia inducible factor-1α (HIF-1α) and vasculoendothelial growth factor (VEGF). Further,the therapeutic effect of anti-angiogenic agents is counteracted by the mobilization of endogenous proangiogenic cells into the tumour microenvironment. In addition to endothelial cells, immune cells play an important role in the microenvironment that regulates tumour growth and response to therapy.
In this review, we highlight some of the recent studies on the importance of immune cells in the microenvironment. The progress in developing combinations of radiotherapy and immunotherapy or other methods for modulation of the tumour immune microenvironment may yield fruitful results in the near future.