IGF1R and breast cancer: It was previously found that down-regulation of IGF-IR using antisense expression vectors may block tumor growth in vivo[12], [13], [14], [15] For example, murine EMT6 breast cancer cells carrying an antisense IGF-IR vector exhibited a significant decrease in cell proliferation in vitro, lost their ability to form colonies in soft agar, and also lost their tumorigenic property when grafted to syngenic mice [16].