Desmethyl erlotinib is a metabolite of erlotinib . Erlotinib is a tyrosine kinase inhibitor which acts on the epidermal growth factor receptor (EGFR), inhibiting EGFR-associated kinase activity (IC50 = 2.5 µM). This inhibits tumor growth in human head and neck carcinoma HN5 tumor xenografts in mice with an ED50 value of 9 mg/kg. Erlotinib also suppresses cyclin-dependent kinase 2 (Cdk2) activity in breast cancer cells (IC50 = 4.6 µM) and JAK2 mutant JAK2V617F positive hematopoietic progenitor cells (IC50 = 5 µM), which is associated with polycythemia vera, idiopathic myelofibrosis, and essential thrombocythemia. Formulations containing erlotinib have been used to treat certain forms of cancer, including non-small cell lung cancer.