Association between obesity-related adipokines and colorectal cancer: A case-control study and meta-analysis

AIM: To examine the association between obesity-related adipokines (adiponectin, leptin, resistin, interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) and colorectal cancer (CRC) risk. METHODS: Serum levels of adipokines were measured in 100 CRC patients and age- and sex-matched controls for the data analysis. Unconditional logistic regression models were used for estimating ORs and 95%CIs related to each adipokine. For the meta-analysis, studies published before July 2013 available on Medline/PubMed and EMBASE were retrieved. The analysis included a total of 17 relevant studies (including the present case-control study): nine studies on adiponectin and eight on leptin. The effect sizes of ORs and 95%CIs were estimated using RevMan 5.1. Heterogeneity was evaluated using Cochran's Q-test and I (2) statistics. RESULTS: Among the five adipokines, only resistin levels were significantly higher in cases than in controls (P < 0.001). The case-control study results showed no association between adiponectin and CRC and a negative association between leptin and CRC. However, the results of the meta-analysis showed a significant inverse association between adiponectin and CRC (OR = 0.91, 95%CI: 0.83-1.00, P = 0.04) and no association between CRC and leptin. After stratification by study design, an inverse association between adiponectin and CRC was observed in prospective studies only (OR = 0.90, 95%CI: 0.82-0.99, P = 0.03), whereas the association between leptin and CRC was inconsistent (prospective studies: OR = 1.14, 95%CI: 1.02-1.27, P = 0.02 and retrospective studies: OR = 0.47, 95%CI: 0.29-0.74, P = 0.001). The associations of resistin and TNF-α with CRC risk were positive, but no association was observed for IL-6. CONCLUSION: Our results suggest a negative association of leptin, positive associations of resistin and TNF-α, and null associations of adiponectin and IL-6 with CRC. However, further studies with larger number of prospective approaches are needed.