Loss of Tumor Suppressor ARID1A Protein Expression Correlates with Poor Prognosis in Patients with Primary Breast Cancer

PURPOSE: Somatic mutations of the chromatin remodeling AT-rich interactive domain 1A (SWI-like) gene (ARID1A) have been identified in many human cancers, including breast cancer. The purpose of this study was to evaluate the nuclear expression of ARID1A in breast cancers by immunohistochemistry (IHC) and to correlate the findings to clinicopathologic variables including prognostic significance. METHODS: IHC was performed on tissue microarrays of 476 cases of breast cancer. Associations between ARID1A expression and clinicopathologic characteristics and molecular subtype were retrospectively analyzed. RESULTS: Low expression of ARID1A was found in 339 of 476 (71.2%) cases. Low expression of ARID1A significantly correlated with positive lymph node metastasis (p=0.027), advanced pathologic stage (p=0.001), low Ki-67 labeling index (p=0.003), and negative p53 expression (p=0.017). The ARID1A low expression group had significantly shorter disease-free and overall survival than the ARID1A high expression group (p<0.001 and p<0.001, respectively). Multivariate analysis demonstrated that low expression of ARID1A was a significant independent predictive factor for poor disease-free and overall survival in patients with breast cancer (disease-free survival: hazard ratio, 0.38, 95% confidence interval [CI], 0.20-0.73, p=0.004; overall survival: hazard ratio, 0.11, 95% CI, 0.03-0.46, p=0.003). In patients with luminal A type disease, patients with low ARID1A expression had significantly shorter disease-free and overall survival rates than patients with high ARID1A expression (p=0.022 and p=0.018, respectively). CONCLUSION: Low expression of ARID1A is an independent prognostic factor for disease-free and overall survival in breast cancer patients and may be associated with luminal A type disease. Although the biologic function of ARID1A in breast cancer remains unknown, low expression of ARID1A can provide valuable prognostic information.