The prognostic significance of the 8th edition AJCC TNM staging system for non-small-cell lung cancer is not applicable to lung cancer as a second primary malignancy

Background and Objectives It is unclear whether the prognostic significance of the 8th American Joint Committee on Cancer (AJCC) tumor, node, metastasis (TNM) staging system for non-small-cell lung cancer (NSCLC) is applicable to lung cancer as a second primary malignancy (LCSPM). This study used a population-based database to evaluate this relationship. Methods Patients diagnosed with second primary lung cancer after a nonpulmonary malignancy were identified from the Surveillance, Epidemiology and End Results (SEER) registry from 2004 to 2015. Cumulative incidence function (CIF) and multivariable CIF regression analyses were performed to estimate the difference in disease-specific mortality (DSM) among different TNM stages. Results Our cohort included 2687 patients from the SEER database. After CIF analysis, although rates of 1-year, 3-year, and 5-year DSM trended higher with increasing TNM stages, the DSM curves overlapped for many subcategories. In a multivariable regression analysis, hazards ratios (HRs) for subcategories of stage Iota demonstrated no significant difference compared with the reference stage Iota A1 ([Iota A2 HR = 1.120; 95% confidence interval [CI], 0.477-2.626]; [Iota A3 HR = 1.762; 95% CI, 0.752-4.126]; [Iota B HR = 2.003; 95% CI, 0.804-4.911]). The following HRs trended higher for increasing TNM stages but with overlapping CIs among adjacent stage groupings. Conclusion The 8th edition AJCC TNM staging system fails to provide accurate prognostic value for LCSPM.