Prostanoids, including PGD2, PGE2, PGF2α, PGI2, and TXA2, activate nine GPCRs, namely PTGDR1, PTGDR2, PTGER1, PTGER2, PTGER3, PTGER4, PTGFR, PTGIR, and TBXA2R. PTGDR1 downregulation by DNA hypermethylation is correlated with colorectal cancer development [26, 27]. Here, PTGER1 is linked to colorectal cancer.