Background: Target therapies and new surgical strategies deeply modify the history of CCLM patients (pts). Several prognostic scoring systems have been developed but no one is able to identify pts who should be excluded from a potentially useless surgery. Currently research is committed in identifying early biomarkers able to discern pts who could benefit from an aggressive approach. Exosomes are arising as promising biomarkers in cancer. The aim of this pivotal study was to analyze the association among exosome levels during CCLM-pts treatment, clinical outcomes and the KRAS status. Methods: We enrolled 22 pts with CCLM candidate to preoperative chemotherapy (pCT) and subsequent liver surgery. A blood sample was collected before pCT, after surgery, monthly during follow-up and at progression (PD). Exosomes were isolated by ultracentrifugation and characterized by standard methods. Exosomes concentration was assessed by Bradford assay. We adopted ddPCR™ KRAS G12/G13 Screening Kit to evaluate the KRAS status in exosomal DNA (e-DNA). Results: 22 CCLM pts received pCT and underwent liver surgery: 5 major hepatectomies and 17 multiple liver resections. Changes in exosomes plasma levels were found to correlate with each treatment step,resulting reduced after pCT and surgery and increased at PD, respectively (p = 0.0026). Pts with higher baseline exosome levels experimented shorter PFS than those with lower levels (p = 0.0033 HR 0.2). No association was found between exosome levels after liver surgery and disease free interval nor overall survival. KRAS status on e-DNA was evaluated on 10 pts in baseline, in pCT, after surgery, and in PD samples. In 8 out of 10 pts e-DNA displayed the same mutational status than the one detected on tumor DNA. Changes in e-DNA KRAS copies were found statistically significant in pCT vs surgery and pCT vs PD (p = 0.039; p = 0.04). Conclusions: Our study suggests a prognostic role of exosome levels in CCLM pts. Moreover, we showed that KRAS mutational status could be monitored during the post-surgery follow up by analyzing e-DNA. Overall, our data confirm the potential role of exosomes in liquid biopsy tool to monitor molecular changes during the treatment of CCLM pts.