GPR15 and cancer: Among all of the 33 cancer types from the TCGA database, cancers with significant differential GPR15 expression (on the basis of difference of median expression between cancer samples and paired normal samples) are COAD (downregulated, p = 3.06 × 10−12) and READ (downregulated, p = 6.80 × 10−4) (Figure 1C, Figure S1).