RAB8A-Mediated Exosomal Cargo Redistribution as a Pre-Metastatic Signature for Patient Stratification in Triple-Negative Breast Cancer

Booth No: M134

Characteristic

Triple-negative breast cancer (TNBC) accounts for 10–15% of breast cancer diagnoses and carries the worst prognosis among all subtypes due to the absence of hormone receptor and HER2 therapeutic targets. A critical clinical gap remains: no non-invasive tool currently exists to identify patients at high risk of distant metastasis before clinical spread occurs.
Using LC-MS/MS TMT-based quantitative proteomics of peripheral blood plasma-derived exosomes from 49 TNBC patients at Stage 1 baseline (metastatic/recurrent n=11, stable n=38), we identified a Rab8A-mediated bidirectional exosomal cargo redistribution (ECR) mechanism occurring prior to clinically detectable metastasis. Patients who subsequently developed metastasis or recurrence exhibited two concurrent, directionally opposing signatures in their circulating plasma exosomal proteome: selective depletion of 67 cytoskeletal and quality-control proteins (Cargo-Loss Panel, CLP₆₇; FC ≤ 0.75, p < 0.05) alongside selective enrichment of 10 metabolic and immune-modulatory proteins (Metabolic-Cargo Enrichment Panel, MCEP₁₀; FC ≥ 1.33, p < 0.05). This bidirectional pattern — concurrent CLP depletion and MCEP enrichment — has no precedent in the literature and is proposed to be coordinated upstream by Rab8A, a vesicular trafficking GTPase. Cancer-specific functional validation was performed in MDA-MB-231 and MDA-MB-468 TNBC cell lines via siRNA knockdown (commissioned assay, NHRI 2023), demonstrating RAB8A-dependent migration suppression absent in non-cancerous HEK293 controls.
To quantify this mechanism at the individual patient level, we derived the Metastatic Cargo Redistribution Score (MCRS = mean[log₂ MCEP₁₀] − mean[log₂ CLP₆₇]), classifying patients as Cargo Redistribution-Positive (CR+, MCRS > 0) or CR-negative. In the discovery cohort, MCRS achieved an AUC of 0.859 (95% CI: 0.694–0.982; one-tailed Mann-Whitney p = 0.000170), with a mean group difference of 1.636. CR+ prevalence was 72.7% among metastatic/recurrent patients versus 13.2% in stable patients, confirming that the cargo redistribution signal is detectable in peripheral blood prior to clinical metastasis.