Expression of RPL9 predicts the recurrence of non-muscle invasive bladder cancer with BCG therapy

Numerous biomarkers and risk tables can be used to predict recurrence or progression of patients with primary or recurrent non-muscle invasive bladder cancer (NMIBC) receiving Bacillus Calmette-Guerin (BCG). However, few are suitable for BCG-unresponsive disease (i.e., recurrence or progression after BCG treatment). Therefore, identification of a novel marker that allows accurate prediction of prognosis, particularly risk of recurrence, is critically important in clinical practice. In the current study, gene ontology and gene set enrichment analyses of microarray datasets (GSE13507, n = 47) revealed that differentially expressed genes in recurred NMIBC patients after BCG treatment were associated with virus and ribosomal pathways. Among the core-enrichment genes, the expression of RPL9, a putative tumor suppressor, was lower in recurred NMIBC patients after BCG therapy than in patients without recurrence (P = 0.033) from the E-MTAT-4321 European cohort (n = 84). Data from The Cancer Genome Atlas (n = 406) showed that bladder cancer patients with higher RPL9 expression had a longer overall survival probability than patients with lower RPL9 expression (P = 0.011). Moreover, we used the latest digital PCR platform to examine 59 NMIBC patients and identified downregulation of RPL9 in patients with recurrence after BCG therapy (P = 0.031). The Kaplan-Meier survival estimator showed that NMIBC patients with higher expression of RPL9 had longer recurrence-free survival (log-rank test, P = 0.015). Therefore, we conclude that RPL9 expression is a prospective predictor of recurrence after BCG therapy in NMIBC patients.