P11.13.B INTRAOPERATIVE DISCRIMINATION OF TUMOR MARGINS IN BRAIN METASTASES USING A LABEL-FREE NANOPLASMONIC BIOSENSOR, A PROOF OF CONCEPT.

Abstract BACKGROUND Complete resection of brain metastases may be challenging in infiltrative lesions lacking a clear tumor-parenchyma border. Current intraoperative tools to discriminate the margins usually need exogenous contrast agents, often have poor resolution and are limited by subjectivity. We evaluated a nanoplasmonic biosensor based on extraordinary optical transmission (EOT) as a label-free, real-time method to discriminate between tumor and peritumoral brain tissue during surgery. MATERIAL AND METHODS In this prospective study, ex vivo tissue samples were obtained intraoperatively from patients with histologically confirmed brain metastases. Paired samples from the edge tumor and adjacent peritumoral tissue were collected, and their nature was confirmed independently by the Department of Pathology. Samples were subsequently analysed using an EOT-based nanoplasmonic biosensor, and their refractive index (RI) values were recorded. A diagnostic threshold was determined based on the distribution of RI values, and classification performance was assessed by calculating the percentage of correctly classified samples. This study is ongoing, and additional cases are being collected to refine the diagnostic threshold and validate these preliminary findings. RESULTS A total of 8 paired tissue samples were analysed. RI values were consistently higher in tumor tissue compared to peritumoral samples (median RI: 1.352 vs. 1.345). Using an empirically determined threshold of 1.347, the biosensor correctly classified 75% of the samples overall. Specifically, it achieved a sensitivity of 87.5% for tumor detection and a specificity of 62.5% for peritumoral tissue identification. These preliminary results suggest that the EOT-based biosensor can differentiate between tumor and peritumoral brain tissue, although further validation with a larger cohort is required. CONCLUSION The EOT-based nanoplasmonic biosensor successfully discriminated ex vivo between tumor and peritumoral brain tissue in brain metastases. These findings are consistent with previous work from our group in glioblastoma using the same biosensor platform. It requires no contrast agents, no tissue processing, and no interpretation by a trained pathologist, providing objective and immediate feedback. These characteristics make it a promising tool for improving intraoperative margin assessment and guiding surgical decision-making in patients with brain metastases.