AbstractDies1/VISTA induces embryonic stem-cell differentiation, via BMP-pathway, but also acts as inflammation regulator and immune-response modulator. Dies1 inhibition in a melanoma-mouse model led to increased tumour-infiltrating T-cells and decreased tumour growth, emphasizing Dies1 relevance in tumour-microenvironment. Dies1 is involved in cell de/differentiation, inflammation and cancer processes, which mimic those associated with Epithelial-to-Mesenchymal-Transition (EMT). Despite this axis linking Dies1 with EMT and cancer, its expression, modulation and relevance in these contexts is unknown. To address this, we analysed Dies1 expression, its regulation by promoter-methylation and miR-125a-5p overexpression, and its association with BMP-pathway downstream-effectors, in a TGFβ1-induced EMT-model, cancer cell-lines and primary samples. We detected promoter-methylation as a mechanism controlling Dies1 expression in our EMT-model and in several cancer cell-lines. We showed that the relationship between Dies1 expression and BMP-pathway effectors observed in the EMT-model, was not present in all cell-lines, suggesting that Dies1 has other cell-specific effectors, beyond the BMP-pathway. We further demonstrated that: Dies1 expression loss is a recurrent event in GC, caused by promoter methylation and/or miR-125a-5p overexpression and; GC-microenvironment myofibroblasts overexpress Dies1. Our findings highlight Dies1 as a novel player in GC, with distinct roles within tumour cells and in the tumour-microenvironment.