Investigations on ductal carcinoma in situ (DCIS, stage 0) have indicated that a shift toward a less active tumor immune environment occurs already at this early tumor stage and in a TGF-β-dependent manner, leading to a restricted infiltration of immune effector cells, accompanied by an increase in the number of regulatory T cells [39]. This evidence concerns the gene TGFB1 and ductal breast carcinoma in situ.