EGFR and non-small cell lung carcinoma: Thus, continuous treatment with erlotinib prescribed to NSCLC patients with overexpression or mutations in EGFR (deletion in 19th exon or L858R point mutation), leads to accumulation of cell clones with T790M mutation in EGFR or up-regulation in other growth receptor signaling pathways (e.g., HGFR, RBB3/PI3K) leading to drug resistance.