For this reason, as a first approach, we questioned whether through their conditioned medium, MSCs could differentially promote the expression of immunoregulatory genes such as IDO, TGF-β, IL-4, and IL-10 in MDA-MB-231 and BT-474 cells lines, which may be crucial to favor the establishment of an immunotolerant state, because the overexpression of these immuno-regulatory genes correlate with a poor prognosis and, generally, are present in advanced tumor stages [36,37,38,39,40]. The gene discussed is IDO1; the disease is neoplasm.