What is the abscopal effect?

In oncology, the abscopal effect refers to the ability of localized radiation to trigger systemic antitumor effects and achieve a systemic tumor response. The abscopal effect has been demostrated in mouse model and observed in human as well.  The abscopal mechanism has been elucidated by the work of many investigators who showed that this process was likely mediated by the immune system leading to immunogenic tumor cell death, a process that involves dendritic cells, T regulatory cells, and suppressor cells as critical mediators. The recent successes of several immune checkpoint inhibitor clinical trials in various malignancies have demonstrated wide applicability and enormous therapeutic potential of immunomodulation and have galvanized keen interest in this field. An ambitious goal of combining radiotherapy and immunotherapy in the clinic would be long-term remission for cancer patients with metastatic disease, perhaps through an approach analogous to delivering an in-situ anti-tumor vaccine.

Find below a cartoon showing the abscopal effect in mouse model where a distant tumor lesion on the right flank disappears after treating with local radiation therapy another distant tumor lesion on the left flank.