Transforming growth factor beta (TGF-β) exhibits complex and context-dependent cellular responses. While it mostly induces tumor-suppressive effects in early stages of tumorigenesis, tumor-promoting properties are evident in advanced disease. This TGF-β duality is still not fully understood, and whether TGF-β supports invasion and metastasis by influencing cancer cells directly, or rather through the stromal tumor compartment, remains a matter of debate. Here, we utilized a library of colorectal cancer (CRC) patient-derived tumoroids (PDTs), representing a spectrum of tumor stages, to study cancer cell-specific responses to TGF-β. Using conditions allowing for the differentiation of PDTs, we observed TGF-β-induced tumor-suppressive effects in early-stage tumoroids, whereas more advanced tumoroids were less sensitive to the treatment. Notably, one tumoroid line harboring an atypical KRASQ22K mutation underwent partial epithelial-to-mesenchymal transition (EMT), which was associated with morphological changes and increased invasiveness. On a molecular level, this was accompanied by elevated expression of mesenchymal genes, as well as deregulation of pathways associated with matrix remodeling and cell adhesion. Our results suggest that tumor cell-intrinsic responses to TGF-β are critical in determining its tumor-suppressive or tumor-promoting effects.

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