The intratumoral heterogeneity of FGFR2-amplified adenocarcinomas of the upper GIT has been investigated in only a few studies using different methods (Ye et al. 2015; Pectasides et al. 2018; Schrumpf et al. 2022; Tokunaga et al. 2016; Kuboki et al. 2018). The gene discussed is FGFR2; the disease is adenocarcinoma.