Only patients without missing data (in terms of the confounding variables) were included by applying sequential filters to the Microsoft Excel database. Contraindications for surgery were divided into 3 categories: a) cardiopulmonary (CP), b) metastasis/non-resectable (M/NR) and c) other. Patients were considered accordingly by an analogy 1/5/1 (paralleling the rates among the 155 patients) in each of the 3 patient classes of the TNM-stage (IIA, IIB/III, IV) which were considered respectively by an analogy of 2/9/7 (paralleling the rates among the 155 patients). These sequential steps reduced the total 155 patients by 8 patients (missing data), 19 patients by "TNM-stage" filtering, 2 patients by "contraindications for surgery" filtering and by 3 patients lost to follow up. The remaining 123 patients were assigned to four groups.