While feeding excess L-glycine marginally promoted growth of ras1G12V;csk−/−,path tumours, L-alanine had no growth-promoting effect in ras1G12V;csk−/−, ras1G12V;csk−/−,path or ras1G12V,CG1139;csk−/− animals (Supplementary Fig. 6c, d, f, g, i–k). Here, CSK is linked to neoplasm.