MMP9 and renal cell carcinoma: Moreover, S.C. Joosten et al.20summarized several mechanisms of sunitinib resistance in RCC patients and identified some potential predictive biomarkers of sensitivity or resistance to sunitinib, such as VEGF, VEGFR, interleukin‐8 (IL‐8), neutrophil gelatinase‐associated lipocalin (NGAL), tumor necrosis factor‐alpha (TNF‐α) and matrix metalloproteinase‐9 (MMP‐9), on the basis of data from current preclinical and clinical studies.