Fibroblast activation protein predicts prognosis in clear cell renal cell carcinoma

Clear cell renal cell carcinoma is a complex disease with only partial response to therapy and scarce reliable clinical parameters indicative of progression and survival. Fibroblast activation protein expression has been correlated with prognosis in several malignancies but never in renal cancer. We aim to analyze the immunohistochemical expression of fibroblast activation protein in 208 clear cell renal cell carcinomas and to evaluate its impact on the prognosis and survival. A positive cytoplasmic immunostaining of this protein in the stromal fibroblasts associated to cancer cells is associated with large tumor diameter (≥4cm), high-grade (G3/4) tumors, and high-stage (≥pT3) tumors. Fibroblast activation protein-positive cases had significantly shorter survivals after 5 (P=.00015), 10 (P=.0000042), and 15 (P=.000043) years of follow-up, with a hazard ratio of 0.31. Multivariate analysis showed that fibroblast activation protein (P=.00117) was stronger than grade and stage in predicting clinical aggressiveness in clear cell renal cell carcinoma. This study confirms the usefulness of fibroblast activation protein detection in the stromal fibroblast associated to cancer in clear cell renal cell carcinoma and adds a new immunohistochemical marker to predict clinical behavior in these patients.