BACKGROUND: Cell cycle proteins are important markers in predicting tumor behavior in urothelial carcinoma of the bladder. The objectives of this study were 1) to determine the expression levels of some of those markers in a series of patients with bladder carcinoma, 2) to define their value in distinguishing T1a (minimally invasive) from T1b (invasive) tumors, and 3) to evaluate their use as predictive factors in the progression of T1a and T1b tumors. METHODS: Tumor specimens from 101 patients were included (22 Ta specimens, 34 T1a specimens, 15 T1b specimens, and 30 T2 specimens). A tissue microarray from the 101 paraffin embedded tissue blocks was constructed. Immunohistochemistry for p16, p27, p21, p53, cyclin D1, and Ki-67 were performed. To evaluate T1a and T1b tumor progression, clinical and follow-up data were available for all 49 patients. RESULTS: Cyclin D1 and p27 were the only markers that showed a significant association with tumor stage and tumor grade (cyclin D1: P = 0.002 and P > 0.00, respectively; p27: P = 0.024 and P = 0.031, respectively). The results indicated that a combination of p21 (odds ratio, 5.7; 95% confidence interval [95% CI], 1.3-24.8 [P = 0.022]) and p16 (odds ratio, 3.7; 95% CI, 0.8-16.5 [P = 0.081]) may have potential use in distinguishing T1b tumors from T1a tumors. Finally, none of the markers examined were found to have predictive value for T1a and T1b tumor progression. CONCLUSIONS: The expression of cyclin D1 and p27 was associated with the most important prognostic factors (tumor stage and grade). The combination of p21 and p16 may have value in distinguishing T1b tumors from T1a tumors, although this finding must be evaluated in much larger series. Finally, none of the markers studied appeared to have predictive value for disease progression in patients with T1a and T1b urothelial bladder tumors.