OAT and gastric cancer: Arginine and proline can be further metabolized into putrescine, spermine, spermidine and other polyamines under the catalysis of OAT, AGMAT, ODC1, SRM, and SMS. Fig. 3a14, a16, a18 illustrate the spatial distributions of putrescine, spermine and spermidine in gastric cancer tissue section, and the results suggest that polyamines are mainly distributed in tumor tissues, followed by epithelium, intestinal metaplasia and lymphoid tissues.