Successful Treatment of Advanced Gastric Cancer with Brain Metastases through an Abscopal Effect by Radiation and Immune Checkpoint Inhibitor Therapy

The abscopal effect refers to the phenomenon in which local radiotherapy is associated with the regression of metastatic cancer that is distantly located from the irradiated site. Here, we present a case of a patient with advanced gastric cancer and brain metastases who was successfully treated with brain radiotherapy and anti-programmed death-1 (PD-1) therapy-induced abscopal effect. Although anti-PD-1 therapy alone could not prevent disease progression, the metastatic lesions in the brain and also in the abdominal lymph node showed a drastic response after brain radiotherapy and anti-PD-1 therapy. To our knowledge, this is the first reported case of successful treatment of advanced gastric cancer with multiple brain and abdominal lymph node metastases, possibly through anti-PD-1 therapy combined with brain radiotherapy-induced abscopal effect. We suggest that the combination of brain radiotherapy and anti-PD-1 therapy may be considered as a therapeutic option for advanced gastric cancer, especially when there is brain metastasis.