P12.02.B CHARACTERIZATION AND PROGNOSTIC EVALUATION OF PSTAT3 EXPRESSION IN PERITUMORAL REACTIVE ASTROCYTES OF BRAIN METASTASES FROM RENAL CELL CARCINOMA
Authors: Interno' V , Bertero L , Pellerino A , Rizzo M , Cazzato G , Messina R , Signorelli F , Rudà R , Tucci M , Soffietti R , Porta C 
Published: September 2023

Abstract

BACKGROUND
The signal transducer and activator of transcription 3 (STAT3) shows a key role in regulating the anti-tumor immune response. STAT3 is activated in cancer cells and in the tumor microenvironment thus inhibiting crucial immune regulators expression and promoting immunosuppressive factors. Brain metastatic cells sustain a pro-metastatic signal through the hyperexpression of pSTAT3 in reactive astrocytes (RAs) surrounding metastases and succeed in generating an immunosuppressive signal resulting in a worsened prognosis. Pre-clinical analyses demonstrated that brain metastases (BMs) size might be reduced by blocking STAT3 signal in RAs. pSTAT3 expression in BMs from renal cell carcinoma (RCC) has never been systematically analyzed. Our study aims to investigate pSTAT3 expression in RCC brain metastatic specimens to identify its therapeutic and prognostic role. Materials and

METHODS
A total of 27 paraffin-embedded human BMs from RCC obtained through surgical resection at the Neurosurgical Units of University of Bari “Aldo Moro” and University of Turin were stained for phosphorylated (Tyr705) STAT3 (pSTAT3) and GFAP, then evaluated and scored by clinical neuropathologists of the University of Turin. Protein expression was semi-quantitatively assessed according to the intensity and the number of positive cells. Overall survival (OS) was intended by the date of BMs onset. A survival curve was generated by grouping patients with high (score 2-3) and low (score 0-1) pSTAT3 in ARs. P values were obtained with the two-sided log-rank test.

RESULTS
97% (26 out 27) of BMs were positive for pSTAT3 (pSTAT3+) in RAs, with 41% of them receiving a score above 1. In detail, 1 scored with 3 (moderate and diffuse expression), 10 (38%) with 2 (moderate focal expression or weak diffuse expression) and 15 (56%) with 1 (weak and focal expression) according to the abundance and signal intensity of pSTAT3 in ARs. The median OS from BM onset was 12 months. After grouping patients by the high or low pSTAT3 expression level, no significant survival differences were evidenced (mOS 10 vs 13 months, p= 0.432).

CONCLUSIONS
Our study represents the first analysis investigating pSTAT3 expression on BMs from RCC. Considering the low number of specimens, which reflects a low rate of surgical resections, our work assumes an exploratory value. RAs surrounding BMs from RCC ubiquitously express pSTAT3, but only 41% of cases with a moderate or diffuse expression seem to be related to a biological pro-metastatic role. Although patients with high pSTAT3 expression showed reduced survival, this result was not statistically significant, possibly due to the limited sample size. If confirmed in larger and prospective cohorts, these data could lay the foundation for new therapeutic strategies involving pSTAT3 signaling inhibition (Silibinin) eventually improving the intracranial response rate.