The diagnosis of lung cancer was established based on clinical criteria and confirmed by pathology reports from surgery, biopsy or cytology samples in approximately 95% of cases, and on clinical history and imaging for the remaining 5%. The date of diagnosis was defined as the date of the first clinical study to report a suspicious lesion (for example, chest X-ray or CT-scan) that led directly to diagnosis. To verify the diagnosis, we examined the clinical history, bronchoscopy and biopsy results, and x-ray and thorax CT scans (and MRI or PET scans when available) and hospital discharge letter for each case. In addition, we reviewed surgery descriptions and pathology reports for the surgical cases, and biopsies and/or cytology reports from brushing, broncho-alveolar lavage, sputum, bronchoaspirate, or pleural or pericardial effusion for the non-surgical cases. All available imaging documenting lymph node and/or distant metastases or other functional/clinical conditions that excluded surgery were also assessed. Tumor histology was coded according to the WHO Histological Typing of Lung and Pleural Tumors (1999); clinical and/or post-surgical staging was performed according to the International System for
