Multi-Protein Profiling Reveals High Nuclear KFL-4 Expression as a Predictor of Poor Overall Survival in Breast Cancer: A Retrospective Cohort Study

Following the establishment of the four molecular subtypes of breast cancer, additional biomarkers are required to further refine prognostication and patient stratification. Krüppel-like factors (KLFs), components of Wnt signaling, estrogen receptor beta (ERβ) isoforms, cyclin D1, and E-cadherin have been implicated in epithelial-mesenchymal transition, tumor proliferation, and disease progression. In this monocentric retrospective cohort study, tissue microarrays from 153 patients with histologically confirmed breast cancer were analyzed by immunohistochemistry to assess the expression of cytoplasmic Dkk1, β-catenin, and E-cadherin, as well as nuclear cyclin D1, KLF-4, KLF-5, and ERβ isoforms, using the Remmele and Stegner immunoreactive score. Associations between protein expression patterns with clinicopathological characteristics and survival outcomes using univariable and multivariable Cox regression analyses were examined. High cytoplasmic E-cadherin expression was associated with improved overall survival [hazard ratio (HR) 0.37, 95% confidence interval (95% CI) 0.18-0.77, <i>p</i> = 0.008], whereas high nuclear expression of KLF-4 (HR 2.63, 95% CI 1.32-5.22, <i>p</i> = 0.006) and KLF-5 (HR 2.16, 95% CI 1.01-4.65, <i>p</i> = 0.048) was associated with reduced overall survival. High ERβ1 expression showed a marginally protective association with the development of metastases (log-rank test <i>p</i> = 0.045). Importantly, nuclear KLF-4 expression remained independently associated with adverse overall survival after adjustment for tumor stage, lymph node status, molecular subtype, and other molecular markers (adjusted HR 4.09, 95% CI 1.93-8.67, <i>p</i> < 0.001). These findings identify nuclear KLF-4 as an adverse prognostic marker in breast cancer and support its potential relevance for molecular patient stratification.