Figure 2(b) depicts the relationship between the error rate and the number of classification trees, and Figure 2(c) shows the final order of relative importance of the first eight genes. Figures 2(d)–2(f) show the expression of these eight genes, HMGCS2, UMOD, DEFB1, NAT8, KCNJ1, TMPRSS2, CLDN19, and AQP2, in the normal and cancer tissues of the TARGET, GSE66405, and GSE73209 datasets. Compared with the normal tissues, these eight genes were consistently downregulated in cancer tissues and were expressed as a significant positive correlation (Figure 2(g)). Here, CLDN19 is linked to cancer.