Size distribution of extracellular vesicles in pretreatment ascites and plasma is correlated with primary treatment outcome in advanced high-grade serous carcinoma.

To improve the treatment outcome and survival of patients with advanced high-grade serous carcinoma (HGSC), prognostic biomarkers for assessing the feasibility of complete (R0) or optimal (R1) primary cytoreductive surgery are needed. Additionally, biomarkers for predicting the response to neoadjuvant chemotherapy (NACT) in patients with primary inoperable disease could help stratify patients for tailored therapy and improve personalised approach. Such promising biomarkers are extracellular vesicles (EVs), which are present in ascites and plasma and are available for minimally invasive liquid biopsy. EV concentration and EV molecular profile have been at the forefront of research in the field of biomarkers for many years now, but recent studies have highlighted the importance of EV size distribution. Our study aimed to evaluate the potential of the EV concentration and size distribution in pretreatment ascites and plasma samples from patients with advanced HGSC as prognostic biomarkers. In our prospective cohort study, nanoparticle tracking analysis (NTA) was used to determine EV characteristics in paired pretreatment ascites and plasma samples from 37 patients with advanced HGSC. Patients were treated with primary cytoreductive surgery followed by adjuvant chemotherapy (ACT) (N = 15) or NACT followed by interval debulking surgery (IDS) when optimal cytoreduction was not feasible (N = 22). The correlations of the EV concentration and size distribution in ascites and plasma with treatment outcome, progression-free survival (PFS) and overall survival (OS) were analysed. We found a significant correlation between the EV size distribution in ascites and residual disease after primary cytoreductive surgery. Larger EVs in ascites correlated with worse resection success after primary cytoreductive surgery. A significant correlation between the D10 value of EVs in plasma and the chemotherapy response score (CRS) after NACT was observed. A smaller D10 value of plasma EVs was correlated with a better chemotherapy response. Receiver operating characteristic (ROC) curve analysis revealed excellent performance for D10 value in ascites for the prediction of suboptimal (R2) resection at primary debulking surgery and excellent performance for D10 value in plasma for the prediction of complete or near-complete chemotherapy response score (CRS 3) at interval debulking surgery. There was a significant correlation between the mean diameter, D90 value and proportion of medium/large (> 200 nm) EVs in ascites and those in plasma. On the other hand, there was no correlation of the EV concentration or D10 and D50 values between the ascites fluid and plasma samples. Our results indicate that the EV size distribution in ascites has the potential to predict resection success after primary cytoreductive surgery and that the EV size distribution of the smallest EVs in plasma might help predict the chemotherapy response of patients treated with NACT. In the future, molecular analyses of size-dependent EV cargo could provide more insight into their biological functions and potential as predictive biomarkers.