Abscopal effect with unknown fever during radiotherapy: Two case reports

The abscopal effect is a rare phenomenon that is defined as regression of tumor lesions distant from irradiation targets. We have experienced two cases with an abscopal effect with unknown fever and an inflammatory response during radiotherapy. Radiotherapy is a local treatment, therefore, it rarely causes systemic side effects during radiotherapy, and if a patient develops a fever during radiotherapy, it is often considered tumor fever. We experienced 2 cases of unknown fever during irradiation followed by abscopal effect. The obvious relationship between the abscopal effect and the unknown fever is not clear. However, Unknown fever during radiotherapy may be a hint to the abscopal effectconsidering that immune response and cytokines closely related to the abscopal effect.