YAP1 and neoplasm: This methylation state is directly associated with the two opposite effects of RASSF4: (1) when the promoter region is hypomethylated, RASSF4 is normally expressed and exerts its tumor-suppressing effect by activating the RAS-dependent apoptosis pathway; (2) in contrast, hypermethylation leads to a reduced RASSF4 level, which in turn triggers abnormal activation of the Hippo–YAP pathway and excessive activation of the RAS/MAPK signaling pathway within cells, driving the malignant progression of tumors.