Establishing a TNM-like risk classification for metachronous second pulmonary adenocarcinoma in patients with previously resected pulmonary adenocarcinoma.

Background: For metachronous second pulmonary adenocarcinoma (msPAD) in patients with resected PAD, the method to distinguish tumour clonality has not yet been well established, which makes it difficult to determine accurate staging and predict prognosis. Methods: Patients received surgery for the primary and encountered msPAD were recruited into the Surveillance, Epidemiology, and End Results database. We extracted overall survival 1 (OS1) for the primary, overall survival 2 (OS2) for the msPAD, and defined interval survival as the interval time between the first and second PAD. Based on the nomogram and recursive partitioning analysis, a tumor, node, metastasis staging system (TNM)-like risk stratification system was established for OS2 on the premise of suspending the dispute of tumor clonality. Results: A total of 1,045 patients were identified. There is no significant association between interval survival and OS2. A TNM-like risk stratification system was established based on the independent pathological factors for prognosis, including tumor diameter (2nd), node metastasis (2nd), grade (2nd), and extrapulmonary metastasis (2nd). The proposed risk stratification system present well capacity in predicting and stratifying prognosis. Compared with the TNM stage system, the proposed risk stratification system presents a smaller Akaike information criterion (AIC) but larger c-index, and generates higher accuracy to predict prognosis at 160 months of follow-up according to the time-dependent receiver operating curve (ROC) curve. Conclusions: In conclusion, the TNM-like risk stratification appears to be suitable for prognostic prediction and risk stratification for msPAD patients with former PAD resection. This model validates and refines the known classification rules based on the easily collected variables, and highlights potentially clinical implications.