RESEARCH Association of Expression of Kruppel-Like Factor 4 and Kruppel-Like Factor 5 with the Clinical Manifestations of Breast Cancer Chih-Jung Chen & Sey-En Lin & Yueh-Min Lin & Shu-Hui Lin & Dar-Ren Chen & Chi-Long Chen Received: 8 December 2010 / Accepted: 26 May 2011 / Published online: 15 June 2011 # Arányi Lajos Foundation 2011 Abstract Kruppel-like factors (KLFs) are import modulators of cell proliferation, differentiation, and transformation and have recently been considered possible prognostic factors in breast cancer. In this study, we investigated the correlation between KLF4 and KLF5 expression and the clinical manifestations of breast cancer by immunohistochemical analysis. We observed increased KLF4 and KLF5 expression in tumor cells (invasive and in situ carcinomas), consistent KLF4 and KLF5 expression in in situ and invasive carcino- mas, significant associations between KLF4 expression and tumor grade (p =0.033), size (p =0.035) and stage (p =0.006), and an association between KLF5 expression and tumor grade (p =0.033). Interestingly, we observed a relationship between increasing age and KLF4 expression (p =0.007), with a tendency towards greater expression in tumor cells in patients over 50 years old. Moreover, KLF5 nuclear localization was restricted to non-tumor breast ducts and lobules; however, loss of nuclear expression of KLF5 in in situ and invasive carcinomas was observed. Although the mechanism of the loss of KLF5 nuclear expression is not clear, this phenomenon may imply a possible tumor- suppressor-like role for KLF5 in breast cancer tumorigenesis. The expression of KLF4 and KLF5 in breast cancer patients in Taiwan is similar to that in Western countries, except for the uncertainty surrounding its prognostic significance. Further clarification of the underlying mechanisms of KLF4 and KLF5 expression and their correlations with breast cancer outcomes is necessary. C.-J. Chen : S.-E. Lin : C.-L. Chen (*) Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, 250 Wu-Xing Street, Taipei 110, Taiwan e-mail: chencl@tmu.edu.tw C.-J. Chen Institute of Medicine, Chung Shan Medical University, Taichuang, Taiwan C.-J. Chen Institute of Medical and Molecular Toxicology, Chung Shan Medical University, Taichuang, Taiwan C.-J. Chen : Y.-M. Lin : S.-H. Lin Department of Surgical Pathology, Changhua Christian Hospital, Changhua, Taiwan C.-J. Chen : Y.-M. Lin : S.-H. Lin Department of Medical Technology, Jen-Teh Junior College of Medicine, Nursing and Management, Miaoli, Taiwan S.-E. Lin : C.-L. Chen Department of Pathology, College of Medicine, Taipei Medical University, Taipei, Taiwan C.-L. Chen Department of Pathology, Wan Fang Hospital, Taipei, Taiwan D.-R. Chen Comprehensive Breast Cancer Center, Department of Surgery, Changhua Christian Hospital, Changhua, Taiwan D.-R. Chen School of Medicine, Chung Shan Medical University, Taichung, Taiwan D.-R. Chen (*) Department of Surgery, Changhua Christian Hospital, 135 Nan-Hsiao Street, Changhua 500, Taiwan e-mail: 115045@cch.org.tw Pathol. Oncol. Res. (2012) 18:161–168 DOI 10.1007/s12253-011-9422-7