EGF receptor inhibitors increase ErbB3 mRNA and protein levels in breast cancer cells

► Treatment of breast cancer cells with EGFR inhibitors leads to ErbB3 upregulation. ► ErbB3 is upregulated both at protein and mRNA levels. ► EGFR inhibitor treatment also leads to upregulation of ErbB2. ► This response might mediate resistance to EGFR-targeted cancer treatment.