Delayed radiation-induced vasculitic leukoencephalopathy related to stereotactic radiosurgery (SRS) of brain metastases has been reported to manifest clinically 9-18 months following treatment. Immune modulating therapies have been introduced to treatment regimens of malignancies with metastatic predilection to the brain. The interaction of these systemic therapies with other modalities of treatment for brain metastases, namely SRS, has not been fully characterized. We report two patients with metastatic malignancies to the brain who received SRS followed by immunotherapy with monoclonal antibodies (mAbs) to programmed death 1 (PD-1). Both patients appeared to have early clinical and radiological progression of their treated lesions, which was highly suspicious for tumor progression. Both patients underwent surgical resection of their lesions and the material was submitted for histopathological examination. Pathological examination in both cases showed predominantly radiation-induced changes characterized by reactive astrocytosis and vascular wall infiltration by T lymphocytes. The accelerated response to SRS in these two patients was temporally related to the initiation of immunotherapy. We propose a possible biological interaction between SRS and the PD-1 mAbs. Additionally, awareness of this potential occurrence is critical for accurate interpretation and proper management of clinical and radiological findings in these patients.
- Received September 28, 2015.
- Revision received December 29, 2015.
- Accepted February 16, 2016.
- Copyright ©2016, American Association for Cancer Research.