EGFR and breast cancer: First, we tested three different signatures of intrinsic resistance to EGFR inhibitors: (1) non-small cell lung cancer (NSCLC) cell lines treated with erlotinib (GSE31625) [49]; (2) breast cancer cell lines treated with erlotinib (GSE12790) [48]; and (3) NSCLC cell lines treated with gefitinib (Coldren et al.