Abscopal Effect following Stereotactic Radiation Therapy to the Brain and Spleen in Metastatic Endometrial Cancer: A Case Report.

Introduction: The abscopal effect of radiation therapy is a rare phenomenon in which immune activation induces the regression of distant, nonirradiated tumors. Recent studies have increasingly suggested that combining radiation therapy with immunotherapy may increase the occurrence rate of the abscopal effect. Case Presentation: We report the case of a 72-year-old woman with stage IA endometrial cancer. After surgery and adjuvant pelvic radiation therapy, oligometastases develop in the spleen and lungs. Subsequently, stereotactic body radiation therapy was initiated for the spleen; nonetheless, it was discontinued because of new brain metastases that caused neurological symptoms. Following brain-fractionated stereotactic radiosurgery, her symptoms improved, and imaging demonstrated a reduction in both brain and splenic lesions. The lung metastases, which had not been irradiated, initially grew but then regressed after 6 months of radiation therapy to the spleen and brain, suggesting an abscopal effect. Of particular interest is the observation that while splenic metastasis increased 8 months after radiation, the multiple lung metastases maintained their reduction. Conclusion: This case highlights that a delayed abscopal effect can develop following stereotactic radiation therapy, even without the use of immune checkpoint inhibitors.