A Case of Lung Cancer That Showed an Abscopal Effect after Irradiation of Simultaneous Oropharyngeal Cancer

Background. The abscopal effect is a phenomenon in which tumor shrinkage occurs outside the radiation field. It usually occurs between the primary tumor and metastatic lesions of the same cancer or between metastatic lesions, and there have been no reports on the abscopal effect occurring after irradiation of other cancer types. Case. A woman in her 50s was diagnosed with double primary cancer of lung and oropharyngeal cancer. After the administration of nivolumab as second-line treatment for lung cancer, the lung cancer did not show any increase in size for six months (stable disease). However, the pharyngeal cancer showed progression, so irradiation was started for it. After radiotherapy, shrinkage of the primary lung cancer (outside the irradiation field) was observed. Conclusion. We experienced a case in which primary lung cancer shrank after irradiation for primary pharyngeal cancer. This case suggests that abscopal-like effects may occur between different cancer types.