Although the expression of Smac/DIABLO has been reported in various cancers, little is known about its clinical significance in bladder cancer. The present study was designed to evaluate the relationship between progression of disease and Smac/DIABLO expression by clinical pathological analysis of patients with bladder cancer. The level of Smac/DIABLO expression was quantified by Western blot analysis using non-fixed fresh frozen tissues derived from patients with bladder cancer. All normal bladders expressed Smac/DIABLO. However, 64/84 (76%) of bladder cancers expressed Smac/DIABLO and 24% were negative. In Ta and T1 superficial bladder cancers, 98% expressed Smac/DIABLO, whereas only 41% expressed Smac/DIABLO in muscle-invasive bladder cancers. Smac/DIABLO expression inversely correlated with the grade of bladder cancer. Patients with Ta and T1 superficial bladder cancer with higher Smac/DIABLO expression had a longer postoperative recurrence-free period than those with lower Smac/DIABLO expression after transurethral resection in the 5-year follow-up. Patients with invasive bladder cancer expressing Smac/DIABLO had a longer postoperative disease-specific survival than those without Smac/DIABLO expression after radical cystectomy in the 5-year follow-up. The cisplatin-resistant T24 bladder cancer line (T24/CDDP) and the adriamycin-resistant T24 line (T24/ADR) showed lower level of Smac/DIABLO expression, compared with the T24 parental line. In conclusion, the present study demonstrates for the first time that Smac/DIABLO expression was downregulated in bladder cancer, especially in high grade muscle-invasive bladder cancer, and that lower Smac/DIABLO expression in bladder cancer predicted a worse prognosis. In addition, the cisplatin-resistant T24/CDDP line and the adriamycin-resistant T24/ADR line expressed lower level of Smac/DIABLO expression. These results suggest that Smac/DIABLO expression in bladder cancer may be used as a prognostic parameter, and that low Smac/DIABLO expression in bladder cancer may be associated with resistance to chemotherapy.

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