SMAD4 and cancer: GSTO2 and MT1M have been described as tumor suppressors in cancer, and SMAD4 is listed as a tumor suppressor gene in the COSMIC Cancer Gene Census (Mao et al., 2012; Sondka et al., 2018; Terayama et al., 2020; Xu et al., 2020; Li et al., 2021, 2023; Sumiya et al., 2022).