A PHASE II MULTICENTRE RANDOMISED, PARALLEL GROUP, DOUBLE-BLIND, PLACEBO-CONTROLLED STUDY OF ZD1839 (IRESSA TM) (250MG TABLET) PLUS BEST SUPPORTIVE CARE (BSC) VERSUS PLACEBO PLUS BSC IN CHEMOTHERAPY-NAÏVE PATIENTS WITH ADVANCED (STAGE IIIB OR IV) NON-SMALL CELL LUNG CANCER (NSCLC) AND POOR PERFORMANCE STATUS