Regression of all untreated lesions in multifocal low-grade meningioma following fractionated stereotactic radiotherapy---abscopal effect or spontaneous regression?. Case report and review of the literature

Abscopal effects have been reported predominantly in metastatic cancers, indicating a radiographic response in a lesion that has not been included in the radiotherapy target volume. The response is interpreted as a humoral immune response to radiotherapy-generated tumour-specific antigens. In this case study, we present the first histologically confirmed multifocal low-grade meningioma with spontaneous regression of all other lesions after conventionally fractionated stereotactic radiotherapy (RT). Two localisations, right frontal and right spheno-orbital, were resected at the time of the initial diagnosis in a 66-year-old woman. RT was performed 1 year later to a progressive occipital lesion at the cerebral falx. Regular magnetic resonance imaging (MRI) showed slightly decreasing tumour volume in untreated lesions 1 year after RT and continued during further follow-up. Up to > 7 years after treatment, MRI demonstrated an almost complete response of all initial lesions. Two prior reports with meningioma were published in one patient with an atypical meningioma after conventionally fractionated RT and another patient with an intracranial meningiomatosis after radiosurgery. This case study supports the concepts of treating only progressive or symptomatic meningioma lesions locally and careful regular MRI surveillance for further assessment. Potential active interventions to trigger an abscopal effect are currently not known. Further research of this beneficial effect for our patients should be supported.