CLDN18 and cancer: Pairwise CLDN biomarker AUC comparisons (heatmap, Figure 2, right panel), across 12 tumor types (The Cancer Genome Atlas; TCGA data), showed that CLDN1 could readily distinguish colon from kidney, brain, lung, and ovary cancers, while both CLDN1 and CLDN4 (but not CLDN18) could distinguish brain from kidney cancer.