This 2 arm study will compare the efficacy and safety of sequential treatment with Tarceva and gemcitabine, and of gemcitabine monotherapy, as first line treatment of elderly patients, or patients with ECOG performance status of 2, with advanced non-small cell lung cancer.Patients will be randomized to receive either sequential gemcitabine 1250mg/m2/day on days 1 and 8 + Tarceva 150mg po on days 15-28 of each 4 week cycle, or gemcitabine monotherapy 1000mg/m2/day on days 1, 8 and 15 of each 4 week cycle. The anticipated time on study treatment is 3-12 months, and the target sample size is 100-500 individuals.