The controversial abscopal effect.

The abscopal effect is potentially important for tumor control and is mediated through cytokines and/or the immune system, mainly cell-mediated immunity. It results from loss of growth stimulatory and/or immunosuppressive factors from the tumor. Until recently, the abscopal effect referred to the distant effects seen after local radiation therapy. However, the term should now be used interchangeably with distant bystander effect. Through analysis of distant bystander effects of other local therapies, we discuss the poorly understood and researched radiation-induced abscopal effect. Although the abscopal effect has been described in various malignancies, it is a rarely recognized clinical event. The abscopal effect is still extremely controversial with known data that both support and refute the concept.