Surgery-Derived Reactive Oxygen Species Produced by Polymorphonuclear Leukocytes Promote Tumor Recurrence: Studies in an In Vitro Model

Surgery for Colorectal Cancer: A Trigger for Liver Metastases Development? New Insights into the Underlying Mechanisms

Surgery is a crucial intervention and provides the best chance of cure for patients with colorectal cancer. Experimental and clinical evidence, however, suggests that paradoxically surgery itself may precipitate or accelerate tumor recurrence and/or liver metastasis development. This review addresses the various aspects of surgery-induced metastasis formation and sheds light on the role of inflammation as potential trigger for metastasis development. Understanding these mechanisms may provide potential new perioperative interventions to improve treatment outcomes, and as such could transform the perioperative timeframe from a facilitator of metastatic progression to a window of opportunity to reduce the risk of liver metastasis development. Ultimately, this can potentially improve long-term survival rates and quality of life in patients with colorectal cancer.

Neutrophils promote liver metastasis via Mac-1-mediated interactions with circulating tumor cells

Although circulating neutrophils are associated with distant metastasis and poor outcome in a number of epithelial malignancies, it remains unclear whether neutrophils play an active causal role in the metastatic cascade. Using in vivo models of metastasis, we found that neutrophils promote cancer cell adhesion within liver sinusoids and, thereby, influence metastasis. Neutrophil depletion before cancer cell inoculation resulted in a decreased number of gross metastases in an intrasplenic model of liver metastasis. This effect was reversed when inflamed neutrophils were co-inoculated with cancer cells. In addition, early adhesion within liver sinusoids was inhibited in the absence of neutrophils and partially restored with a short perfusion of isolated activated neutrophils. Intravital microscopy showed that cancer cells adhered directly on top of arrested neutrophils, indicating that neutrophils may act as a bridge to facilitate interactions between cancer cells and the liver parenchyma. The adhesion of lipopolysaccharide-activated neutrophils to cancer cells was mediated by neutrophil Mac-1/ICAM-1. Our findings, therefore, show a novel role for neutrophils in the early adhesive steps of liver metastasis.

The perioperative period is an underutilized window of therapeutic opportunity in patients with colorectal cancer

OBJECTIVE

In this review, we address the underlying mechanisms by which surgery augments metastases outgrowth and how these insights can be used to develop perioperative therapeutic strategies for prevention of tumor recurrence.

SUMMARY BACKGROUND DATA

Surgical removal of the primary tumor provides the best chance of long-term disease-free survival for patients with colorectal cancer (CRC). Unfortunately, a significant part of CRC patients will develop metastases, even after successful resection of the primary tumor. Paradoxically, it is now becoming clear that surgery itself contributes to development of both local recurrences and distant metastases.

METHODS

Data for this review were identified by searches of PubMed and references from relevant articles using the search terms "surgery," "CRC," and "metastases."

RESULTS

Surgical trauma and concomitant wound-healing processes induce local and systemic changes, including impairment of tissue integrity and production of inflammatory mediators and angiogenic factors. This can lead to immune suppression and enhanced growth or adhesion of tumor cells, all of which increase the chance of exfoliated tumor cells developing into secondary malignancies.

CONCLUSIONS

Because surgery remains the appropriate and necessary means of treatment for most CRC patients, new adjuvant therapeutic strategies that prevent tumor recurrence after surgery need to be explored since the perioperative therapeutic window of opportunity offers promising means of improving patient outcome but is unfortunately underutilized.