The investigators assume that progression-free survival mean time for patients treated with vinorelbine will be 3 months, and for patients treated with gemcitabine plus vinorelbine will be 5 months. That implies a reduction in risk ratio of 40% (Hazard ratio = 1,67). Assuming a bilateral alpha error of 0.05 and beta error of 10%, and the number of events needed if 60% of patients have progressed after 1 year, the number of patients needed per treatment arm is 114. Considering a 10% post-randomization drop-out, the final number of patients is 252 (126 per arm).