Erlotinib induces the increase of cetuximab and trastuzumab binding sites. Calu-3, H322 and H292 cell lines were treated with erlotinib for 24 h. Binding sites were assessed by flow cytometry using cetuximab (Calu-3, H322) and trastuzumab (H292) as primary antibodies followed by PE-anti-human IgG exposure. Binding sites quantification is reported as Molecules of Equivalent Fluorophore [MEF]. The results in A, B, C are from representative experiments. Each experiment, repeated three times, yielded similar results.