Further evidence of the importance of this pathway as a target for ATRA in epithelial carcinogenesis comes from a recent study that showed that ATRA could suppress proliferation of esophageal cancer cells through activation of retinoic acid receptor β2 (RAR-β2); and that this effect coincided with a suppression of EGFR/Erk/AP1 signaling and suppression of cyclooxygenase 2, a proinflammatory enzyme that is over-expressed in several cancer types [38]. This evidence concerns the gene PTGS2 and cancer.