ESTRO 2024 - Abstract Book

S5199

Radiobiology - Microenvironment

ESTRO 2024

for CD4, CD8, F4/80, CD31, phospho-STAT3, and GFAP were performed. As part of a validation study, we identified 11 patients who underwent SRS for BMs and subsequently developed symptomatic RN or tumor recurrence, requiring brain surgery. Hematoxylin-eosin-stained tissue samples were independently reviewed by two neuropathologists and partitioned into compartments including tumor, necrosis and surrounding gliotic brain. Subsequently, multiplex was performed to detect astrocytes (GFAP), microglia and circulating macrophages (CD68). Phosphorylation of STAT3 (Tyr705) was used to identify microglia and reactive astrocytes, and to analyze the proportion of activated cells in the brain microenvironment and in the RN lesions.

Results:

The histological analysis of RN lesions in mice revealed structural disorganization of the brain, cellular loss, and increased vascularization with presence of aberrant blood vessels and areas with blood extravasation secondary to the destabilization of the blood–brain barrier (BBB). Nissl staining showed a significant (p<0.01) neuronal loss in the irradiated brain hemisphere compared to the controls. The quantification by IHC showed a significantly higher endothelial damage (CD31+) and infiltration of macrophages (F4/80+), astrocytes (GFAP+), CD4 and CD8 T lymphocytes in RN, perinecrotic areas and irradiated hemisphere when compared to the non-irradiated brain. Phosphorylated STAT3 was significantly higher in RN area compared to the non-irradiated brain (p<0.001). Multiplex immunofluorescence confirmed a high number of reactive astrocytes (GFAP+ pSTAT3+) and reactive microglia (F4/80+ pSTAT3+) in RN and the irradiated hemisphere. Analysis of human brain specimens showed that astrocytes and microglia were actively phosphorylating STAT3 in the areas corresponding to RN and gliosis. The tumoral compartments were solely positive for infiltrating and activated macrophages (CD68+/pSTAT3+).