What is the Role of the Neutrophil: Lymphocyte Ratio in Colorectal Cancer?

The composition and cell-to-cell interactions of the peripheral immune compartment are known to influence outcomes in multiple disease entities, both neoplastic and otherwise. There is an ongoing search for a reliable biomarker in the peripheral immune compartment that can predict outcomes in colorectal cancer, given its high mortality rates. The neutrophil:lymphocyte ratio (NLR) has been suggested as one such marker, given its accessibility. This review discusses the current evidence behind the use of the NLR in predicting different aspects of colorectal cancer (CRC) behaviour, from survival to recurrence, metastasis, tumour biology, response to therapy and CRC complications. We also discuss the debate in the literature surrounding the use of other peripheral immune compartment biomarkers compared with the NLR for this purpose and ideas for future research.