Elevated expression of microRNAs 155, 203, 210 and 222 in pancreatic tumors is associated with poorer survival

Pancreatic cancer is the eighth most common cancer and has an overall 5-year survival rate lower than 10%. Because of their ability to regulate gene expression, microRNAs can act as oncogenes or tumor-suppressor genes and so have garnered interest as possible prognostic and therapeutic markers during the last decade. However, the prognostic value of microRNA expression in pancreatic cancer has not been thoroughly investigated. We measured the levels of miR-155, miR-203, miR-210, miR-216, miR-217 and miR-222 by quantitative RT-PCR in a cohort of 56 microdissected pancreatic ductal adenocarcinomas (PDAC). These microRNAs were chosen as they had previously been shown to be differentially expressed in pancreatic tumors compared to normal tissues. The possible association of microRNA expression and patients' survival was examined using multivariate Cox's regression hazard analyses. Interestingly, significant correlations between elevated microRNA expression and overall survival were observed for miR-155 (RR = 2.50; p = 0.005), miR-203 (RR = 2.21; p = 0.017), miR-210 (RR = 2.48; p = 0.005) and miR-222 (RR = 2.05; p = 0.035). Furthermore, tumors from patients demonstrating elevated expression levels of all 4 microRNAs possessed a 6.2-fold increased risk of tumor-related death compared to patients whose tumors showed a lower expression of these microRNAs. This study provides the first evidence for an oncogenic activity of miR-155, miR-203, miR-210 and miR-222 in the development of pancreatic cancer as has been reported for other tumor types. Furthermore, the putative target genes for these microRNAs suggest a complex signaling network that can affect PDAC tumorigenesis and tumor progression.