Classification of recurrence patterns in surgically treated non-small cell lung cancer - A systematic review and a call for standardization

Background: Despite significant advancements in early detection and treatment, cancer recurrence remains a major challenge, affecting 30–55 % of patients within two years following surgery. Tumor recurrence is commonly classified as local, locoregional, regional or distant, yet a unified consensus on these definitions is still lacking. Materials and methods: A systematic review of the recent literature (2020–2024) was conducted in accordance with PRISMA guidelines to collect site-specific recurrence definitions. A general descriptive analysis was performed to assess agreement across studies on how recurrence patterns are interpreted. Results: A total of 3082 articles focused on surgically treated NSCLC between 2020 and 2024 were screened and 112 met the eligibility criteria, with 36 papers specifically comparing lobar and sublobar resections. Recurrences at the surgical margins, the bronchial stump, and the ipsilateral nodes were consistently classified as either local or locoregional. Conversely, recurrences in the opposite lung or in the interscalene nodes were mostly classified as distant. However, recurrences in a different ipsilateral lobe, nodal recurrences in the contralateral hilum and mediastinum, in the chest wall and in the pleural spaces were variably classified as local, locoregional, regional or distant relapses. Conclusions: This review demonstrates significant inconsistencies and lack of uniformity in the definitions of recurrence patterns of surgically treated non-small cell lung cancer. This variability has relevant consequences for the comparability of results across different studies. Establishing standardized and consistent definitions is paramount for enhancing research quality, clinical decision-making, and patient outcomes.