HAAO and nonpapillary renal cell carcinoma: A consistent and significant decrease in the number of QPRT peptides identified, and in normalised (LFQ) peptide intensities (representing relative quantification), was seen in ccRCC tissues compared with normal kidney tissues, and similar findings were observed for other enzymes of the kynurenine pathway, namely 3-hydroxyanthranilite 3,4-dioxygenase (HAAO) and kynurenine 3-monoxygenase (KMO) (Fig. 3a).