The clinical and prognostic value of miR-9 gene expression in Tunisian patients with bladder cancer

There is a major need for the identification of biomarkers, which are able to guide personalized therapy for bladder cancer, in particular after resection of the primary tumor. Specifically, miR-9 upregulation has been preliminarily associated with a more aggressive phenotype of bladder cancer, namely muscle-invasive bladder cancer (MIBC) or high-grade non-muscle-invasive bladder cancer (HG NMIBC). In order to explore the potential utility of miR-9 as a biomarker in bladder cancer, we have investigated its expression pattern in a sample of Tunisian patients who have undergone primary resection. This is a retrospective study performed on BCa samples from 90 patients (44 specimens of HG NMIBC, 23 specimens of LG NMIBC, and 23 specimens of MIBC). Ten samples from the non-tumoral zone of cystectomy specimens were used as controls. For each specimen, we measured miR-9 expression and correlated it with the clinical characteristics of the patients. Overall, miR-9 was overexpressed in MIBC compared to NMIBC specimens (median fold change [FC]: − 8.89 vs 1.41, p = 0.001). Similarly, miR-9 expression was significantly different in LG NMIBC, HG NMIBC and MIBC subgroups (median FC: 0.68, 2.14 and 8.89, respectively; p = 0.001). ROC analysis showed that miR-9 expression pattern could be used as potential biomarker for distinguishing NMIBC subgroups: indeed miR-9 expression is relatively low in LG NMIBC and high in HG NMIBC. The thresholds are estimated at 0.063 and 21.597, respectively. Moreover, miR-9 was associated with a higher risk of progression. This study suggests the clinical value of miR-9 as a prognostic factor in bladder cancer after tumor resection. Should the prognostic ability of miR-9 be confirmed in larger studies, also on different ethnic groups, it would be useful to investigate whether urine sampling—which is easier to perform, less invasive and less costly—can provide the same results as analysis on surgical specimens.