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 carcinomas, 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 tumorsuppressor-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.
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