Histopathology of brain metastases after radiosurgery.

Histopathological investigations revealed acute-, subacute-, and chronic-type tissue responses, accompanied by inflammatory cell reaction in radiosurgery treated cerebral metastases originating from different primary cancers. Immunohistochemistry demonstrated that the preponderance of CD68-positive macrophages and CD3-positive T lymphocytes in the inflammatory infiltration developed in better controlled metastases ( > 5 months). In contrast, it was sparse or absent in poorly controlled neoplasms ( < 5 months) after radiosurgery. This inflammatory reaction may be stimulated by the ionizing energy, probably influenced by the general condition of the patients' immune system as well, and seems to play a role in local tumor control after focused radiation.