[7][8][9] The U.S. Food and Drug Administration (FDA) approved erlotinib for the treatment of locally advanced or metastatic non-small cell lung cancer that has failed at least one prior chemotherapy regimen.

[13] In November 2005, the FDA approved erlotinib in combination with gemcitabine for treatment of locally advanced, unresectable, or metastatic pancreatic cancer.

[14] As with other ATP competitive small molecule tyrosine kinase inhibitors, such as imatinib in CML, patients rapidly develop resistance.

[15] Approximately 20% of drug resistance is caused by amplification of the hepatocyte growth factor receptor, which drives ERBB3 dependent activation of PI3K.

Erlotinib specifically targets the epidermal growth factor receptor (EGFR) tyrosine kinase, which is highly expressed and occasionally mutated in various forms of cancer.

These then use the molecule of ATP to trans-phosphorylate each other on tyrosine residues, which generates phosphotyrosine residues, recruiting the phosphotyrosine-binding proteins to EGFR to assemble protein complexes that transduce signal cascades to the nucleus or activate other cellular biochemical processes.

[citation needed] In India, generic pharmaceutical firm Cipla is battling[when?]