Estrogen receptor β expression and colorectal cancer: a systematic review and meta-analysis

Background Estrogen receptor (ER) is a potential tumor-suppressor gene in colorectal cancer (CRC). This hypothesis is supported by clinical and laboratory observations. Aim In this meta-analysis, we looked at studies that investigated the relationship between ER protein expression and CRC, comparing the lesion with normal adjacent mucosa. Methods English medical literature searches were performed for ER expression in patients with CRC, tumor tissue versus normal mucosa. Searches were performed up to 31 May 2015, using MEDLINE, PubMed, EMBASE, Scopus, and CENTRAL. Meta-analysis was carried out using Comprehensive Meta-analysis Software. Pooled odds ratios and 95% confidence intervals were calculated and ER expression was compared in individual studies using the fixed-effects model. Results The odds ratio of ER expression was 0.216 (95% confidence interval 0.152-0.307, P<0.0001), lower in cancer tissue than normal mucosa. Funnel plot did not indicate a significant publication bias. There was no significant heterogeneity in the studies included: Q=5.897, d.f.(Q)=9, I-2=0.000, P=0.750. Conclusion In this meta-analysis, we confirm the observation of decreased ER expression in CRC. Our results support the hypothesis of ER being a tumor-suppressor gene in the large bowel, and the ER protein protects against carcinogenesis and development of CRC when activated by estrogen. Further studies are needed to examine the potential of selective/specific ligands to activate ER without the side effects found with estrogen and without activating ER. Summary In this meta-analysis, we looked at studies that investigated the relationship between CRC and ER expression in the tumor and normal mucosa of CRC patients. English medical literature searches were performed for studies comparing ER expression in the cancer and normal colonic mucosa in patients with CRC. Meta-analysis was carried out, pooled odds ratios were calculated, and ER expression was compared in individual studies. Copyright (C) 2015 Wolters Kluwer Health, Inc. All rights reserved.