Extracellular Vesicles as Novel Biomarkers for Tumor Association in Intermediate-Risk Paraneoplastic Neurologic Syndromes.

Paraneoplastic neurologic syndromes (PNS) are cancer-related neurologic disorders caused by an autoimmune response targeting both the tumor and the nervous system. Identifying new biomarkers for early cancer detection could improve treatment outcomes. Tumor-derived cells release extracellular vesicles (EVs) carrying tumor-specific molecular signatures, which can help distinguish patients with cancer even in early stages. The aim of this study was to assess the potential of EVs as biomarkers to enhance cancer detection in patients with PNS. This observational and multicenter study included 27 patients with tumor-associated PNS, 26 with suspected PNS without a tumor, 35 with cancer, and 32 healthy controls. Subsequently, among the patients with PNS, individuals were subclassified according to the PNS-Care Score as definite, probable, possible, and non-PNS. Total EVs were isolated from blood by precipitation and from B cells, T cells, and neurons by immunoisolation. To identify a biomarker for diagnostic refinement and clinical stratification, EV levels, size, and protein content were compared across study groups. To find a tumor biomarker in intermediate-risk cases, the possible association between EV protein content and cancer detection in intermediate-risk syndromes was analyzed. Patients with tumor-associated PNS showed significantly higher circulating EV levels compared with those with suspected PNS without evidence of a tumor (p = 0.028). Moreover, total EV levels, along with B cell-derived EVs, effectively differentiated patients with definite PNS from those with probable (p = 0.05) and possible (p = 0.006) PNS. A cutoff value of 2.10 × 1010 particles/mL EVs was identified, above which diagnosis of PNS was definite, with 86% sensitivity and 81% specificity. Proteomic analysis identified specific proteins, including ACADM, HPT, ACTBL, and CCAR2, as markers of definite PNS, differentiating such patients from those with probable and possible PNS, contributing to diagnostic refinement for clinical stratification. It is important to note that increased levels of EVs and CD44 distinguished intermediate-risk cases with tumors from those without. EVs may act as tumor biomarkers in patients with PNS, even in intermediate-risk cases. This study provides Class IV evidence that higher circulating blood levels of EVs can distinguish between tumor-associated PNS from suspected PNS without tumor.