Interestingly, co-culture of macrophages with breast cancer cells whose ID4 expression has been inhibited by siRNA transfection (si-ID4#1, si-ID4#2) led to a significantly attenuated ID4 induction in macrophages, compared to co-culture with control cells (si-SCR) (Figure 2A–D). This evidence concerns the gene ID4 and breast carcinoma.