Ex vivo counting of organs and tissues at 90 min after injection showed a significantly higher accumulation of all cCPE-based radiotracers in claudin-4–expressing PSN-1 tumor xenografts than in HT1080 controls ([111In]In-cCPE194–319: 2.7 ± 0.8 vs. 0.4 ± 0.1 %ID/g, P < 0.001; [111In]In-cCPES313A: 2.3 ± 0.9 vs. 0.5 ± 0.1 %ID/g, P < 0.01; [111In]In-cCPES307A+N309A+S313A: 2 ± 0.4 vs. 0.3 ± 0.1 %ID/g, P < 0.01; [111In]In-cCPED284A: 2 ± 0.2 vs. 0.7 ± 0.1 %ID/g, P < 0.05; [111In]In-cCPEL254F+K257D: 6.3 ± 0.9 vs. 0.7 ± 0.2 %ID/g, P < 0.001) (Fig. 4B). The gene discussed is CLDN4; the disease is neoplasm.