We first traced glutamine metabolites in multiple nude mice carrying xenograft tumors formed by isogenic HCT116 PIK3CA-WT-only CRC cells (where the mutant PIK3CA allele was inactivated) in the left flank or PIK3CA-mutant-only (with the PIK3CA WT allele inactivated) CRC cells15 in the right flank (Fig. 2A,B). The gene discussed is PIK3CA; the disease is colorectal carcinoma.