Clinical and biological relevance of enhancer of zeste homolog 2 in triple-negative breast cancer.

The polycomb group protein, enhancer of zeste homolog 2, is a transcriptional repressor involved in cell cycle regulation and has been linked to aggressive breast cancer. We examined the clinical and biological significance of enhancer of zeste homolog 2 expression in triple-negative breast cancers. Tissue microarrays were constructed with invasive breast cancer cases and stained with the enhancer of zeste homolog 2, cytokeratin 5/6, epidermal growth factor receptor 1, and p53. The expression of these markers was correlated with clinicopathologic variables and patients' outcome. Furthermore, in vivo enhancer of zeste homolog 2 gene silencing was achieved using small interfering RNA incorporated into chitosan nanoparticles. Of 261 cases of invasive breast cancer, high expression of the enhancer of zeste homolog 2 was detected in 87 (33%) cases, and it was strongly associated with a triple-negative breast cancer phenotype (P < .001) compared with all other non-triple-negative breast cancers. Furthermore, high enhancer of zeste homolog 2 was significantly associated with high histologic grade (P = .01), estrogen receptor negativity (P < .001), progesterone receptor negativity (P < .001), epidermal growth factor receptor positivity (P = .04), and high p53 expression (P < .001). Survival analysis demonstrated that patients with high enhancer of zeste homolog 2 had a poorer overall survival compared with those with low enhancer of zeste homolog 2 (P = .03), and it retained its significance as an independent prognostic factor (P = .02). In addition, enhancer of zeste homolog 2 gene silencing resulted in a significant reduction in tumor growth (P < .01) in the orthotopic MB-231 mouse model of breast carcinoma. Our results show that high enhancer of zeste homolog 2 expression is significantly associated with triple-negative breast cancer and decreased survival. Enhancer of zeste homolog 2 may represent a potential therapeutic target for this aggressive disease, which warrants further investigation.