This is a non-interventional, observational, multicenter and retrospective study. Being limited to the collection of patient data already filled in the Tumor Thoracic Registry data base and the data from stage IIIA clinical trials case report forms.

This is a non-interventional, observational, multicenter and retrospective study that will not under any circumstances interfere in the physician's normal clinical practice. Being limited to the collection of patient data already filled in the Tumor Thoracic Registry (TTR) data base and the data from stage IIIA clinical trials case report forms, it does not entail any diagnostic or therapeutic procedure outside of normal clinical practice.

The primary objective is to assess pathological response after neoadjuvant treatment as a subrogate endpoint for overall survival and disease-free survival in resectable stage IIIA non-small cell lung cancer patients.

It is estimated that around 15-20 Spanish sites are enrolling patients with these characteristics in the TTR or in the stage IIIA clinical trials of the Fundación GECP.

Pathologists and physician's of these sites will be invited to participate in the PLANET study as all cases will be clinical-pathologically re-evaluated to reach the study objectives. Each pathologist will re-evaluate the specimens from the selected patients under common criteria.The sample size would be 150 patients enrolled in the study.

Inclusion Criteria:

• Patients with resectable stage IIIA disease (according to American Joint Committee on Cancer [AJCC] lung cancer edition 7 or 8) who were included in the Tumor Thoracic Registry data base and in stage IIIA clinical trials which the sponsor is Fundación GECP.
• Patients with histologically N2 involvement confirmed
• Patients diagnosed as stage IIIA from 2010 and 2017
• Patients who have received neoadjuvant platinum-based treatment and surgery
• Age ≥ 18 years at time of study entry
• PET /TC at diagnosis

Exclusion Criteria:

• Patients who received chemoradiotherapy neoadjuvant treatment
• Patients who were not resected after neoadjuvant treatment
• Patients who were diagnosed after June 2017

The study will include all resectable stage IIIA patients who have received platinum-based neoadjuvant treatment and surgery and that were diagnosed as stage IIIA from 2010 to 2017.The cohort of patients identified for the current study will be based on a portion of patients included in the Thoracic Tumor Registry (TTR) and in stage IIIA clinical trials approved by Spanish Health Authorities which the sponsor is Fundación GECP.