TGFB1 and breast carcinoma: This paradox is also becoming obvious during TGF-β crosstalk with the small GTPase, RAC1, and its splice isoform, RAC1b, in PDAC (Figure 1) and mammary carcinomas (7) contributing to an antagonistic regulation of TGF-β-mediated growth arrest and migratory effects in normal and tumorigenic tissues (8, 9).