The binding of CCL5 to its specific receptor onbreast cancer cells further activates downstream signals to promote the migrationand invasion of breast cancer cells [33].This positive-feedback loop between MSCs and cancer cells implies that theapplication of MSCs in cancer treatment must be carried out with extreme caution.Another example of the tumor promoting effect of MSC has been reported by Shinagawaet al. [34]. Here, CCL5 is linked to breast carcinoma.