CA9 and renal cell carcinoma: Although there are various urinary proteins in experimentation for RCC diagnosis, e.g., carbonic anhydrase 9 (CA9), neutrophil gelatinase-associated lipocalin, Raf-kinase inhibitory protein, nuclear matrix protein-22, aquaporin-1, 14-3-3 protein β/α, perilipin-2, etc., however, none of these have been approved for clinical use due to low sensitivity and reproducibility, or due to lack of experimental validation [85].