Role of the mTOR Pathway in the Progression and Recurrence of Bladder Cancer: An Immunohistochemical Tissue Microarray Study

PURPOSE: Numerous trials have been conducted to develop new treatment regimens for superficial and invasive bladder cancer, because there is an urgent need to identify novel agents to prevent the recurrence and progression of these cancers. We evaluated the prognostic and biological significance of mTOR pathway-related markers in patients with bladder cancer who had undergone transurethral resection of their bladder tumors and radical cystectomy. MATERIALS AND METHODS: We retrieved 208 bladder cancer specimens collected from patients between 1989 and 2007 and constructed a tissue microarray comprising 208 tumor samples and 25 benign urothelium samples. Immunohistochemical staining was performed for mTOR, phosphorylated (phos) S6, and phos4E-BP1. The pattern, percentage, and intensity of staining for all three markers were evaluated. RESULTS: The median age at diagnosis of the patient cohort was 67 years (range: 29-87 years), and the median follow-up was 72 months (range: 1-257 months). The expression of phos4E-BP1 was higher in the bladder cancer cohort than in the benign cohort, whereas phosS6 expression was lower in the bladder cancer cohort than in the benign cohort. The expression of phosS6 was significantly higher in high-grade bladder cancer (p<0.01). There was a significant positive correlation between the H-scores of mTOR and phos4E-BP1 (coefficient of correlation, r=0.37, p<0.01) as well as between the H-scores of mTOR and phosS6 (r=0.17, p<0.05). In the multivariate analysis, strong phosS6 expression predicted shorter progression (p<0.01; hazard ratio [HR], 2.516) and disease-specific survival (p<0.01; HR, 2.396) but not overall survival (p=0.112), whereas strong phos4E-BP1 expression was a predictor of disease-specific survival (p<0.05; HR, 2.105). Moreover, strong phosS6 expression predicted shorter recurrence-free (p<0.05) and progression-free (p<0.05) survival in the superficial bladder cancer cohort. CONCLUSIONS: Our results demonstrate that mTOR pathway activation, as assessed by phos4E-BP1 phosphorylation, is related to bladder cancer tumorigenesis and that S6 protein phosphorylation is associated with a high level of disease recurrence and progression and poor cancer-specific survival.