Table 1: Favoring effect of MSCs on tumors.

AuthorMSC origin Tumor modelMSC: tumor cell ratioOutcomesMechanisms

Chaturvedi P et al. [17]Human bone marrow-derived MSCsBreast( MDA-MB-231, MDA-MB-43)1:1 coinjectionIncreased metastasisactivation of the hypoxia-inducible factors (HIFs)

Walter, M. et al. [21]Human adipose stromal cells (ASCs)Human breast cancer cell line MCF-71:1 coinjectionIncreased migration and invasionSecretion of IL-6

Tsai, Kuo–Shu et al. [22]Human bone marrow-derived MSCsHuman colorectal cancer cell line HT-291:100 coinjectionPromoted tumor sphere formation and tumor initiationIL-6 secreted by MSCs signaled through STAT3

Zhang, Ting et al. [23]Human fetal bone marrow stem cells (hBM-MSCs)4T1 mouse mammary tumor cell line1:1 coinjectionIncreased tumor growthNeovascularization (secretion of macrophage
inflammatory protein-2, vascular endothelial growth factor, transforming growth factor-beta and IL-6)

El-Haibi, Christelle P. et al. [24]Human bone marrow-derived MSCsMDA-MB-231 and MCF7/Ras breast cancer cells1:1 coinjectionEnhanced metastasisIncreased de novo production of lysyl oxidase (LOX)

Patel, Shyam A. et al. [25]Human bone marrow-derived MSCsHighly aggressive MDA-MB-231 breast adenocarcinoma, low-invasive MCF-7 breast adenocarcinoma, T47D breast adenocarcinoma, P815 murine mastocytoma1:1 (T47D and MSCs 2 × 105 /ml each) were added in 500 μl volumes to attain a 50:1 ratio of mononuclear fractions (PBMC)/MSC and PBMC/T47DProtected breast cancer cells from immune clearanceThrough Tregs, inhibited NK cell and CTL functions

Chandler, Emily M. et al. [26]Human adipose-derived stem cells (ADSCs)MCF-7 and MDA-MB-2311:1 co-injectionPromoted tumorigenesis and angiogenesisBidirectional signaling;
ADSCs differentiated into cancer-associated myofibroblasts

Gonzalez, Maria E. et al. [27]Human breast cancer metastatic sites-derived MSCsBreast cancer cell lines MDA-MB-231, MCF7, and MDA-MB-436MSCs were orthotopically injected into the mammary fat pads (1 × 106 cells/mouse)Loss of DDR2 in MSCs impaired their ability to promote DDR2 phosphorylation in BC cells, as well as
BC cell alignment, migration, and metastasis
Reduced migration and metastasis