Prognostic significance of let-7b expression in breast cancer and correlation to its target gene of BSG expression

Let-7 microRNAs (miRNAs) are found in a wide range of species, and alterations of let-7 miRNA family member expression levels in humans are associated with various types of cancer. However, few researchers have reported alterations in let-7b levels in breast cancer (BC). Specifically, the use of altered let-7 expression as a prognostic biomarker is of particular interest and significance. The aim of this study was to investigate whether let-7b could be used as a biomarker of tumor progression and patient prognosis in BC and to determine the target gene of let-7b. We retrospectively analyzed the clinical pathological characteristics of 80 BC. We utilized digoxigenin-labeled locked nucleic acid-miRNA probes to detect let-7b expression in 80 BC and 22 benign breast disease (BBD) histologic specimens by in situ hybridization, and also detect the expression of BSG—a potential target gene of let-7b—by immunohistochemistry. We observed that the levels of let-7b expression in BBD were higher than in BC specimens (P < 0.05), indicating that let-7b could inhibit growth and facilitate differentiation of BBD. Also, loss of let-7b expression on BC tissue specimens raised the possibility that let-7b could play a crucial role in the pathogenesis of BC. Furthermore, let-7b expression in breast cancer patients was inversely associated with tumor lymph node metastasis (P = 0.001), patient overall survival (P = 0.027), relapse-free survival (P = 0.016), and BSG protein expression (P = 0.001). Breast cancer patients with low let-7b expression had poor prognoses, indicating let-7b might act as cancer suppressor gene in BC development and progression by inhibiting the expression of BSG.