Human bone marrow mesenchymal stem cells (hBMMSCs) were shown to transform into tumor-associated fibroblasts (TAFs) when in the vicinity of breast cancer tumors and played an important role in tumor enhancement and metastasis. In early human development MSCs migrating from the yolk sac and aorta-gonad-mesonephros (AGM) via the umbilical cord to the placenta and back to the fetal bone marrow were shown to get trapped in the gelatinous Wharton's jelly of the umbilical cord. The common origin of the Wharton's jelly MSCs and the finally homed hBMMSCs prompted us to evaluate whether hWJSCs are also involved in TAF transformation. hWJSCs and hBMMSCs were grown in the presence of breast and ovarian cancer cell conditioned medium (MDA-TCM, TOV-TCM) for 30 days. No changes were observed in the hWJSCs but the hBMMSCs transformed from short to thin long fibroblasts, their proliferation rates increased and CD marker expression decreased. The transformed hBMMSCs showed positive staining for the tumor-associated markers FSP, VEGF, EGF, and Tn-C. Real-time PCR and multiplex luminex bead analysis showed upregulation of TAF-related genes (FSP, FAP, Tn-C, Tsp-1, EGF, bFGF, IL-6, α-SMA, VEGF, and TGF-β) for hBMMSCs with low expression for hWJSCs. The luciferase assay showed that hWJSCs previously exposed to MDA-TCM or TOV-TCM had no stimulatory growth effect on luciferase-tagged MDA or TOV cells unlike hBMMSCs. The results confirmed that hWJSCs do not transform to the TAF phenotype and may therefore not be associated with enhanced growth of solid tumors making them a safe MSC for cell based therapies. J. Cell. Biochem. 113: 1886–1895, 2012. © 2012 Wiley Periodicals, Inc.