To determine the relevance of IGF-IR in our model of brain metastasis, we first characterized the activation profile of IGF-IR in parental MDA-MB-231 (231P) and parental BT474 M1 breast cancer cells for comparison to their respective brain-seeking sublines, MDA-MB-231Br (231Br) [17] and BT474Br3. This evidence concerns the gene IGF1R and breast carcinoma.