Purpose: Signal transducer and activator of transcription 3 (STAT3) is known to have an important role in cytokine and growth factor signaling pathways. In various types of human malignant tumors STAT3 has been shown to be constitutively activated due to aberrant production of cytokines and growth factors. We examined the presence of STAT3 activation and its association with pathological features and clinical outcome in renal cell carcinoma cases.

Materials and methods: We examined 48 paraffin embedded renal cell carcinoma specimens and corresponding nonneoplastic kidney tissues for the activation status of STAT3 on immunohistochemistry using anti-phospho-specific (p)-STAT3 antibody, which recognizes only activated STAT3. Based on the percent of cells with positive nuclear staining the activation status of STAT3 was determined and categorized into 2 groups, including low-less than 10% and high-90% or more tumor cells positive. The associations of the activation status of STAT3 with pathological features and clinical outcome were analyzed.

Results: Of 48 tumors 24 (50%) demonstrated high levels of nuclear immunostaining for p-STAT3, while the other 24 (50%) showed low levels. Adjacent nonneoplastic kidney tissues showed only little immunostaining for p-STAT3. A significant association of high levels of p-STAT3 with metastasis was observed (p = 0.0094). No significant associations of p-STAT3 immunostaining with pathological stage or grade were observed. A high level of p-STAT3 was a significant indicator of a poor prognosis on univariate and multivariate analysis (p = 0.0117 and 0.0439, respectively)

Conclusions: Our results indicate a high frequency of STAT3 activation in renal cell carcinoma, especially in metastatic disease. STAT3 activation was an independent prognostic variable in renal cell carcinoma cases. Our results strongly suggest that the activation of STAT3 contributes to the development and progression of renal cell carcinoma.