Peripheral monocyte counts predict the clinical outcome for patients with colorectal cancer: a systematic review and meta-analysis

Monocytes originating from bone marrow play a key role in the inflammatory response. Divergent findings regarding the prognostic value of inflammatory factors like absolute monocyte count (AMC) in colorectal cancer (CRC) exist in the current literature. Thus, we sought to perform a systemic meta-analysis to comprehensively estimate whether the peripheral AMC affects the clinical outcome of CRC patients. A comprehensive literature search was performed in PubMed, Web of Science and EMBASE last updated to 23 December 2018, to identify studies reporting the prognostic value of AMC in patients with CRC. Hazard ratios and corresponding 95% confidence intervals (CIs) or P values were used as the effect size estimates for clinical outcomes including overall survival (OS), disease-free survival (DFS), cancer-specific survival (CSS) and progression-free survival (PFS) with the random-effect inverse variance weighted method. The potential heterogeneity was assessed with Q test and I-2 statistics. Subgroup analyses with respect to some clinicopathological parameters were conducted. A total of 16 clinical studies comprising 3826 patients were included for analysis. Pooled analyses revealed that CRC patients with elevated AMC were significantly associated with worse OS (hazard ratio = 1.708, 95% CI: 1.480-1.971, P < 0.001), DFS (hazard ratio = 1.817, 95% CI: 1.289-2.560, P = 0.001), CSS (hazard ratio = 1.551, 95% CI: 1.187-2.027, P = 0.001) and PFS (hazard ratio = 1.487, 95% CI: 1.259-1.756, P < 0.001). In addition, subgroup analyses provided more information and demonstrated the prognostic effect of elevated preoperative AMC in patients with CRC. There were no significant heterogeneity and publication bias. In conclusion, elevated AMC seems to be served as an unfavorable and robust predicative indicator in CRC patients.