PDP1 and nonpapillary renal cell carcinoma: The labelling ratio of citrate m+2 (that is, the fraction of citrate molecules containing two 13C nuclei) to pyruvate m+3 was lower in ccRCC samples than in adjacent kidney, indicating a reduced contribution of glucose through the pyruvate dehydrogenase (PDH) reaction (Fig. 1b,c; isotopologues are in Supplementary Table 4).