SMAD3 and gastric cancer: There are several signaling pathways involved in gastric cancer development and progression, including Wnt/beta-catenin (Nunez et al., 2011), Hedgehog (Yao et al., 2019), TGF-β/SMAD3 (Li et al., 2021), MAPK (Zhang et al., 2014), and PI3K/AKT/mTOR (Chen et al., 2018; Wu et al., 2019) signaling pathway.