Abstract 3359: Distinct profile of peritoneal lavage fluid extracellular vesicles in gastrointestinal carcinomatosis

Abstract Introduction: Gastrointestinal peritoneal carcinomatosis (GI PC) poses significant diagnostic and therapeutic challenges. The commonly used diagnostic tools such as circulating tumor DNA have poor sensitivity in PC. Recent evidence suggests that peritoneal cavity small extracellular vesicles (EV) play a critical role in peritoneal metastasis development and progression. We sought to compare the peritoneal lavage fluid (PL) EV profile (quantity and gene expression) to non-cancer PL to identify the potential of PL EV testing as a liquid biopsy in PC. Methods: PL samples were collected from GI PC patients and non-cancer patients. The inclusion criteria for the non-cancer cohort were BMI 18-30, no cancer/autoimmune history, and had a non-inflammatory indication for surgery (ex. hernia repair). EVs were isolated by precipitation and characterized via nanoparticle tracking analysis (NTA), cryo-electron microscopy (cryo-EM), and western blot. Size distribution (0.5-199.5nm, 200.5-500.5nm) and concentration were quantified by NTA. EV RNA was profiled using NanoString PanCancer Panel (770 genes). Differential expression used log2 fold change ≥1.5 or ≤-1.5 and p≤0.05. Results: A total of 66 PL samples were collected (35 cancer and 31 non-cancer). Of the 31 non-cancer PL, only 19 samples had EV pellets, indicating that in the rest of the samples there were too few EVs to result in an EV pellet. However, all cancer PL had an EV pellet. NTA of the samples that had adequate EV showed that the total quantity of EV (as ×105 particles/mL) was approximately two-fold higher in cancer samples compared to the non-cancer cohort (10.9 × 105 vs. 4.5 × 105; p=0.0005). The difference between the cancer and non-cancer PL EV quantity was retained even after systemic therapy (9.7 × 105 vs. 4.5 × 105; p=0.0002). Cryo-EM demonstrated distinct structural differences of EV between the groups, with cancer-derived EVs exhibiting multilayered, multicompartment, and cargo-dense structures, whereas non-cancer samples predominantly contained simple monolayer vesicles. Gene expression profiling demonstrated significant overexpression of genes involved in epithelial-mesenchymal transition, metastasis, cell-cycle regulation, angiogenesis, and extracellular matrix organization (STAB1, PRF1, CCDC80, SPARCL1, VHL, RHOA) in the cancer cohort compared to the non-cancer cohort. Conclusion: Our study represents one of the largest studies of PL comparison of GI PC to non-cancer. In GI PC the amount of EV and the biophysical and molecular signatures are distinctly different from the non-cancer group. PL EV can be developed into a liquid biopsy in GI PC to fill a critical clinical need. Citation Format: Fatemeh Tajik, Vinodh Kumar Radhakrishnan, Alex N. Dang, Aaqil M. Khan, Melanie Roman, Shaun Daly, Areg Grigorian, Cristobal Barrios, Sigrid Burruss, Maheswari Senthil. Distinct profile of peritoneal lavage fluid extracellular vesicles in gastrointestinal carcinomatosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3359.