A case of lung adenocarcinoma in which radiotherapy to the metastatic lesion resulted in shrinkage of the primary lesion,suggesting an abscopal effect

A 58-year-old woman was diagnosed with lung adenocarcinoma（cT4N0M1c Stage IVB）with multiple bone metastases. Radiotherapy（30 Gy/10 fr）was administered to the metastatic lesions in the lumbar spine, right pelvis, and femur for symptom relief. CT scan after local radiotherapy showed marked reduction of the lung lesions, despite the absence of anti-tumor drug therapy. There was no further increase in tumor size, and the patient is being followed without treatment. Previous reports have shown that the abscopal effect, in which the lesion shrinks in a different area than the irradiated area after radiotherapy, is known. This is thought to be due to the induction of a systemic tumor-specific anti-tumor immune response by local radiation therapy. In recent years, similar cases have been reported in combination with immune checkpoint inhibitors and local radiotherapy, but cases in which the primary tumor shrinks with local radiotherapy alone are extremely rare.