Correlation of miRNA expression profiling in surgical pathology materials, with Ki-67, HER2, ER and PR in breast cancer patients

Background: New molecular markers related to prognosis and/or clinical outcome have been extensively studied in breast cancer. In particular, microRNA (miRNA) has attracted the interest of both basic and clinical investigators as one of the promising molecular markers of breast cancer patients. MiRNAs are a class of short noncoding RNAs that regulate mRNAs at posttranscriptional level and are deregulated in various human malignancies. Previous studies have reported that miRNAs were stably conserved in 10% formalin-fixed paraffin-embedded tissues without significant degradation, in contrast to more fragile RNA. Methods: Therefore, in this study, we examined 21 surgical breast cancer specimens using the Human Cancer microRNA PCR Array system (QIAGEN) to explore potential molecular targets of miRNAs. Results: Profiling of miRNA expression in archival materials demonstrated that a group of deregulated miRNAs was associated with clinicopathological parameters of the patients, such as Ki-67, HER2, ER and PR. For instance, an abundant expression of multiple let-7 miRNA family, also known as tumor suppressor, was detected in low Ki-67 and HER2 groups. Elevated expression of 8 miRNAs overlapped between Ki-67+/HER2+/ER+/PR+ groups, including several known oncogenic miRNAs such as miR-148b, miR-15b, miR-200c, miR-150, miR-191, miR-96, miR-25 and miR-21. Conclusions: These results all indicated that when analyzing miRNAs in surgical pathology specimens of breast cancer as a biomarker, they should be examined as a cluster through miRNA profiling, rather than relying on the analysis of a single miRNA.