Immunohistochemical expression of retinoblastoma protein and p16 in renal cell carcinoma

The regulation proteins retinoblastoma protein (pRb) and p16 play an important role in the cell cycle as tumor suppressors. pRb is the main substrate for the function of cyclin-dependent kinases during the cell cycle in the transition from G(1) to S phase. In this study, the immunohistochemical expression of pRb and p16 in renal cell carcinoma (RCC) were examined.

Paraffin-embedded specimens from 94 patients with RCC were examined immunohistologically, using primary antibodies for p16 and pRb (Novocastra) and a biotin-conjugated anti-mouse IgG secondary antibody. Microscopically, the expression of p16 and pRb was evaluated by examination of the staining intensity of 100 cells of each specimen, and compared with epidemiological parameters (tumor size, TNM, nuclear grade and follow-up). Statistical analyses were conducted by SPSS, version 15.0 (SPSS® Inc., Chicago, Ill., USA), the χ(2) test (Fisher's exact test), the Kaplan-Meier method and Mantel's log rank test.

All 94 tumors showed a positive reaction for pRb (weakly positive in 67.0%; strongly positive in 33.0%). p16 was expressed in only 52.1% (weakly positive in 48.9%; intermediately positive in 3.2%; no strongly positive expression). The expression of p16-positive tumors was significantly associated with the expression of pRb (p = 0.040). Tumor size, grading, lymph node and distant metastases did not correlate with p16/pRb expression.

pRb and p16 control the cell cycle as tumor suppressors. Therefore, in many tumors they are dysregulated. There are distinct differences in expression in various individual RCC. However, in a limited number of cases there was no significant correlation with clinical parameters.