In addition to directly killing tumor cells, exposure to radiation can cause tumors cells to release “eat-me” and danger signals resulting in a type of cell death that induces an immune response. During the process of immunogenic cell death, the endoplasmic reticulum (ER) becomes stressed, which leads to the phosphorylation of eIF2γ. Then calreticulin and disulphide isomerase ERp57, both of which are usually contained in the lumen of the ER, translocate to the cell surface, followed by surface expression of heat shock proteins (HSP) 70 and HSP 90. Dying tumor cells also release the nuclear factor high-mobility group box 1 (HMGB1). This results in engulfment of dead cell particles by immature dendritic cells (DCs) and their subsequent maturation and activation. Activated DCs express toll like receptors (TLR), upregulate antigen presenting molecules (MHC class I & II, CD1d), and express high levels of costimulatory molecules. Expression of these proteins on DCs promotes the cross-priming of tumor antigens and can lead to the induction of a potent anti-tumor immune response.