Abscopal effect of radiation on multiple lung metastases of lung adenocarcinoma: a case report

Background: Abscopal effect is the out-of-field response to localized irradiation therapy that results in systemic antitumorigenic effects such as the regression of a tumor distant from the target site. Case presentation: A 76-year-old woman was diagnosed with pulmonary adenocarcinoma (cT1bN0M0 stage IA), and right upper lobectomy was performed in November 2015. The pathological stage was pT1bN2M0 stage IIIA. Genomic analysis revealed an EGFR mutation. Immunohistochemical analysis revealed a programmed death-ligand 1 tumor proportion score of <1%. The patient was under watchful observation without adjuvant chemotherapy. Multiple mediastinal and right hilar lymph node metastases were found in February 2018. Radiation therapy at a total dose of 60.0 Gy distributed in 30 fractions was performed over a period of 6 weeks. A computed tomography (CT) scan performed 6 weeks after irradiation therapy showed a reduction in lymph node metastases. However, left hilar and right supraclavicular lymph node metastases and multiple pulmonary metastases were newly observed outside of the irradiation field. A CT scan performed 6 weeks later showed a dramatic complete disappearance of the previously observed pulmonary metastases. No chemotherapy was administered during the period. Conclusion: This was a case of abscopal effect: irradiation of the mediastinum resulted in the disappearance of multiple pulmonary metastases in both lungs.