BDNF and renal cell carcinoma: From the 27 cytokines modulated by sunitinib identified by the cytokine array, five (TNF-α, MMP-9, ICAM-1, BDNF, and SDF-1) were selected for further quantitative analysis by ELISA in the whole patient series, based on statistical significance and on biological plausibility of the involvement of such cytokines in renal cell carcinoma.