Pure abscopal effect in a patient with advanced uterine carcinosarcoma

The abscopal effect is a rare phenomenon, in which tumor shrinkage in the nonirradiated metastatic region is observed after radiotherapy. Certainly, this response is sometimes reported with the combined use of immune-checkpoint inhibitors, but a pure abscopal effect is extremely rare, especially in endometrial cancer. We present the case of a 79-year-old woman with an advanced endometrial carcinosarcoma. She was treated with surgical reduction of the primary lesion, followed by radiotherapy of the metastatic regional lymph nodes. Distant metastases were detected in radiological imaging test 2 months after the completion of radiotherapy, and we carefully followed up without any treatment considering the patient's tolerability for further procedures. Six months after recurrence, she experienced cytoreduction in the metastatic lesions confirmed through imaging findings, which was believed to be an abscopal effect, and maintained this shrinking state for 15 months. Herein, we describe this pure abscopal effect from the perspective of imaging, pathological and molecular findings, and therapeutic strategies.