**1. Introduction**

Lung cancer is the most commonly diagnosed cancer and the leading cause of cancer death in the world. In 2018, an estimated 2.1 million new cases (1,368,524 in men and 725,352 in women) of lung and bronchial cancer were diagnosed, and 1.8 million individuals (1,184,947 in men and 576,060 in women) were expected to die of the tumor [1]. Despite recent advances in molecularly targeted therapy and immunotherapy, the long-term survival of patients with lung cancer remains poor, and the five-year-survival rate is below 20% [2,3]. While more than 80% of tumors were unresectable, surgical resection is the major treatment modality for curative intent, with the five-year survival rate being about 60% [4].

The most important prognostic factor for lung cancer is the stage at presentation, which also guides the clinical management of these patients. Based on a global database of lung-cancer cases assembled by the International Association for the Study of Lung Cancer (IASLC) [5], the eighth edition of the American Joint Committee on Cancer (AJCC) staging system for lung cancer was published in 2017 [6], and it was implemented in clinical practice worldwide in 2018 [7]. In addition to the reclassification of extra-thoracic disease into M1b and M1c, the most significant change distinguishing the eighth edition from the seventh edition is the modification of T classification, which may result in different stage allocations. In the eighth edition, stages T1–T4 are redefined according to tumor size (T1a ≤ 1 cm; 1 cm < T1b < 2 cm; 2 cm < T1c < 3 cm; 3 cm < T2a < 4 cm; 4 cm < T2b < 5 cm; 5 cm < T3 < 7 cm; T4 > 7 cm). For patients with former stage IIIA-N2 disease, the reclassification of tumor size more than 5 cm shifting from T2b to T3 (> 5 cm but < 7 cm) and from T3 to T4 (> 7 cm) results in a change of stage from IIIA to IIIB.

Due to heterogeneous disease entity, the role of surgical resection for patients with former stage IIIA-N2 non-small-cell lung cancer (NSCLC) remains controversial. According to the guidelines [7,8], multidisciplinary team assessment prior to treatment is warranted to evaluate the resectability, depending on single N2 lymph node station involvement and/or small lymph node size (<3 cm). The treatment options include resection, followed by adjuvant chemotherapy; induction therapy, followed by surgery; definitive concurrent chemoradiation; and consolidation therapy with Durvalumab. However, despite the complexity in treatment planning and major changes in T description and stage allocation of the eighth edition, the guidelines do not address the consequent changes to treatment algorithms for patients with clinical stage IIIA-N2 NSCLC. Furthermore, the role of surgical resection with curative intent in such patients has not been well evaluated. Hence, the aim of this study was to evaluate the clinical features and surgical–pathological factors that affect the prognosis of patients with resected stage IIIA-N2 NSCLC.
