DDR1 and breast cancer: Indeed, in all three breast cancer cell lines, MCF-7, MDA-MD-157 and BT-474, DDR1 silencing by a pool of four specific siRNA oligos (Figure 3a) was associated with marked inhibition of cell viability as assessed by the MTT assay (Figure 3b) and cell cycle progression (Figure 3c), both in unstimulated cells and after treatment with either insulin or IGF-2.