Afatinib is a anilino-quinazoline derivative and irreversible antagonist of the receptor tyrosine kinase epidermal growth factor receptor family, with antineoplastic activity. Afatinib selectively and covalently binds to and inhibits the epidermal growth factor receptors 1 (ErbB1; EGFR), 2 (ErbB2; HER2), and 4 (ErbB4; HER4), and certain EGFR mutants, including those caused by EGFR exon 19 deletion mutations or exon 21 (L858R) mutations. This may result in the inhibition of tumor growth and angiogenesis in tumor cells overexpressing these kinases. Additionally, afatinib inhibits the EGFR T790M gatekeeper mutation which is resistant to treatment with first-generation EGFR inhibitors. EGFR, HER2 and HER4 are RTKs that belong to the EGFR superfamily; they play major roles in both tumor cell proliferation and tumor vascularization and are overexpressed in many cancer cell types. Afatinib is a substrate and an inhibitor of P-gp and of the transporter BCRP. Co-administration of P-gp inhibitors can increase afatinib exposure while co-administration of chronic P­gp inducers can decrease afatinib exposure.