A large number of prostate cancer (PCa) patients receive treatment without significant benefits, strengthening the need for accurate prognosis, which can be supported by the study of miRNAs. In silico specificity analysis was performed for the identification of miRNAs able to regulate KLK2 and KLK4 expression. Total RNA was extracted from prostate tissues obtained from PCa and benign prostate hyperplasia patients. Thereafter, RNA was polyadenylated and reverse transcribed to cDNA, which was used for qPCR analysis. miR-378 was predicted to target both KLK2 and KLK4 and down-regulated levels detected in PCa patients (p = 0.050). The reduction of miR-378 was correlated with higher Gleason score (p = 0.018), larger diameter tumors (p = 0.034), and elevated serum PSA (p = 0.006). Regarding prognosis, miR-378 was able to improve risk stratification according to Gleason score or tumor stage, while higher risk to recur highlighted for the patients expressing lower miR-378 levels. Finally, the loss of miR-378 was able to predict the short-term relapse of 'high'-and 'very high'-recurrence-risk patients, independent of Gleason score, tumor stage, PSA, and age as indicated by Kaplan-Meier survival curves (p = 0.030) and multivariate Cox regression analysis (p = 0.018). In conclusion, loss of miR-378 expression increases the risk for PCa progression and relapse, despite active treatment.
