By including all patients, open or VATS, and comparing cohorts instead of the surgical technique used, the selection bias is absent. We compare three cohorts. In the first (20007-2009) almost all patients where operated through a thoracotomy. In a second cohort, (2010-2011) the experience with vats was early. In the third period (2012-2013), a standardized vats technique with extensive intrapulmonary and mediastinal lymphadenectomy was used.