The Suppressor Of Cytokine Signaling 1 (SOCS1) has been extensively investigated in immune cells where it works as a potent inhibitor of inflammation by negative feedback regulation of the cytokine-activated JAK–STAT signaling pathways. SOCS1 is also recognized as a tumor suppressor in numerous cancers and its critical functional relevance in non-immune cells, including epithelial cells, has just begun to emerge. Most notably, conflicting results from clinical and experimental studies suggest that SOCS1 may function as either a tumor suppressor or a tumor promoter, in a cell context-dependent manner. Here, we present an overview of the mechanisms underlying SOCS1 function as a tumor suppressor and discuss the emerging evidences of SOCS1 activity as an oncogene.