Related to Fig. 1. a, Summary of the melanomas used in this study and their spontaneous metastatic behaviour after subcutaneous transplantation into NSG mice. Melanomas were characterized as inefficient or efficient metastasizers. Before subcutaneous tumours grew to 2.5 cm in diameter (when the mice were killed per approved protocol), inefficient metastasizers rarely formed macrometastases or micrometastases beyond the lung, whereas efficient metastasizers commonly formed macrometastases as well as micrometastases in several organs (data reflect results from one to five independent experiments per melanoma). Some of these data have been published previously24. b–g, Isotope tracing was performed in NSG mice subcutaneously xenografted with efficiently metastasizing melanomas from four patients (M405, M481, M487 and UT10) and inefficiently metastasizing melanomas from nine patients (M715, UM17, UM22, UM43, UM47, M498, M528, M597 and M610). The number of tumours or mice analysed per treatment is indicated. b, Glutamine m + 5 as a fraction of total plasma glutamine in mice infused with [U-13C]glutamine (14 independent experiments). c, Isotope enrichment in subcutaneous tumours after [U-13C]glutamine infusion (14 independent experiments). d, Glucose m + 6 as a fraction of total plasma glucose in mice infused with [U-13C]glucose (20 independent experiments). e, Plasma glucose and lactate concentrations before and after infusion. f, Lactate m + 3 as a fraction of total plasma lactate in mice infused with [U-13C]lactate (23 independent experiments). g, Lactate m + 1 as a fraction of total plasma lactate in mice infused with [2-2H]lactate (three independent experiments). h, Expected isotope labelling after [2-2H]lactate infusion. i, Western blot analysis of LDHA and LDHB in subcutaneous tumours from NSG mice xenografted with efficiently (M405, M481 and UT10) or inefficiently (UM17, UM43 and UM47) metastasizing melanomas (representative of four independent experiments). Data are mean ± s.d. Statistical significance was assessed using Mann–Whitney tests (c) and t-tests at 180 or 300 min when tumours were obtained for analysis (b, d, f, g) or paired t-tests (e).