Immunohistochemical study of the expression of cell cycle regulating proteins at different stages of bladder cancer

Purpose: The cell cycle is known to be deregulated in cancer. We therefore analyzed the expression of the cell cycle related proteins p21, p27, p16, Rb, and L-myc by immunohistochemical staining of bladder tumors. Methods: The tissue material consisted of bladder tumors from three groups of patients; group 1, 23 patients with recurrent stage Ta (non-invasive) tumors; group 2, 22 patients presenting at their first admission with T2-4 (muscle invasive) tumors; group 3, 24 patients who experienced disease progression from Ta or T1 (invasive in connective tissue) to a higher stage. By immunohistochemical staining the protein expression was compared to allelic deletions of the corresponding genes. The allelic deletions were detected by PCR-based microsatellite analyses. Results: We detected a significant reduction in the expression levels of the cell cycle related proteins p21(waf1) (P=0.002), p27(kip1) (P=0.03), Rb (P=0.00002), and L-myc (P=0.00000007) in muscle invasive tumors compared to noninvasive tumors. Tumors presenting as muscle invasive at first diagnosis had significantly lower levels of p16/CDKN2A (P=0.01) when compared to muscle invasive tumors that followed Ta or T1 precursor lesions. We found no general correlation between allelic deletion of a gene and its immunohistochemical protein expression, indicating that the remaining allele may be capable of encoding a normal or even increased protein level. Conclusions: Our results support the hypothesis that bladder tumors with invasion at first diagnosis differ from those in which invasion follow superficial tumors. This difference is reflected as a different level in cell cycle related protein expression. The data also indicate that allelic deletions of cell cycle related genes do not correlate with an altered level of protein expression.