This open-label, single arm study will assess the correlation between Tarceva (erlotinib)-induced rash and efficacy in patients with inoperable, locally advanced, recurrent or metastatic non-small cell lung cancer (NSCLC) receiving first-line therapy for advanced disease. Patients will receive Tarceva at a dose of 150 mg daily orally, with dose adjustments according to protocol depending on toxicity. Anticipated time on study treatment is until disease progression occurs.