 Patients with disseminated EGFR M NSCLC referred to a participating oncology department may be enrolled in the project. The investigators expect to include 200 patients over a two-year period. Patients will receive standard lines of treatment and follow up. Standard 1st line treatment for these patients is erlotinib. A biopsy and blood sample will be retrieved before treatment with is initiated. The patient will be monitored prospectively with blood samples every 3rd-6th week both during erlotinib treatment, subsequent lines of treatment and treatment intermissions. The blood samples are analyzed for subtypes of EGFR M both sensitizing mutations and mutations known to drive resistance to erlotinib treatment. In the event of occurring resistance mutations or unexpected increase in quantity of sensitizing mutations clinical action will be taken; initially in the form of additional scans searching for signs of disease progression. Clinical data will be retrieved from the patients medical journal. Patients are followed until death or at least 24 months after inclusion. Any excess biological material will be stored for up to 15 years in a bio bank for future research purposes. 