Exosomal survivin as a liquid biopsy biomarker in cancer.

BACKGROUND: Survivin, an inhibitor of apoptosis protein, is a tumour-associated protein linked to poor outcomes in cancer. Increasing evidence suggests that survivin is released by cancer cells within exosomes, meaning conventional serum measurements may underestimate its true circulating levels. Practical approaches to quantify exosomal survivin are therefore required to support its clinical utility as a liquid biopsy biomarker. METHODS: Exosome-enriched small extracellular vesicle (sEV) preparations were concentrated from conditioned media of HCT116 and MDA-MB-231 cancer cell models and from serum samples of 15 cancer patients and 5 healthy controls using polyethylene glycol (PEG) precipitation; Hs68 fibroblasts served as a low-survivin non-malignant control during lysis optimisation. Samples were analysed with and without membrane lysis prior to survivin measurement by ELISA RESULTS: 1% NP-40 was the most effective tested detergent condition for membrane lysis, significantly improving survivin detection in cancer conditioned media (MDA-MB-231: 5.77 ± 0.61 vs 4.45 ± 0.41 ng/mL, p = 0.0348; HCT116: 14.55 ± 2.21 vs 8.30 ± 0.31 ng/mL, p = 0.0083) and patient serum (plain: 102.4 ± 7.63 vs 90.03 ± 9.35 pg/mL, p = 0.0309; PEG-precipitated: 132.7 ± 42.13 vs 102.7 ± 25.35 pg/mL, p = 0.0068). PEG precipitation enhanced exosomal marker recovery, as demonstrated by increased syntenin-1 expression. CONCLUSIONS: NP-40 combined with PEG precipitation significantly improves survivin detection in cancer samples. This practical approach can support quantification of exosome-associated survivin and may be adapted to other exosome-associated proteins in translational cancer research, pending validation in larger cohorts with orthogonal EV characterisation.