Design : Prospective national observational multicenter study. All patients with clinical N2/3 disease based on CT and/or PET requiring invasive mediastinal staging will primarily undergo invasive mediastinal staging with endosonography (EBUS +/- EUS). A subsequent cervical mediastinoscopy will be performed in case no mediastinal lymph node involvement was found with endosonography. Local surgeons perform these procedures according to their institutional practice. Thoracotomy with mediastinal lymph node dissection will be the gold standard for invasive mediastinal staging, in case no mediastinal lymph node metastases were found during clinical staging including endosonography and mediastinoscopy.