IGF1R and breast cancer: It is evident that a discrepancy appears to exist between data showing that IGF1R is commonly overexpressed and confers good prognosis in breast cancer and in the in vitro demonstration that blockade of IGF1R signaling by the use of monoclonal antibodies significantly inhibits IGF‐I‐induced proliferation of breast cancer cell lines (Arteaga et al., 1989; Cullen et al., 1990).