In the present study, we examined whether IRS-1 can associate with other erbB family members, notably erbB3, and whether this has a direct impact on IGF-IR signalling in three ER+ breast cancer cell lines (MCF-7, T47D and BT-474) previously shown to express IRS-1 protein [42-44]. The gene discussed is EGFR; the disease is breast carcinoma.