Background: Thymic epithelial tumor (TET) staging has been based on Masaoka-Koga systems or the 8th edition of the TNM classification, which do not use tumor size as a T descriptor. The 9th edition of the TNM classification incorporates tumor size; however, the study on which this classification is based included only 4.4% of patients from North America. This study investigated the prognostic impact of primary tumor size in TET patients in the US population.
Methods: Using data from the National Cancer Database (NCDB), we analyzed patients with surgically resected TETs diagnosed in 2004-2020. Survival analysis was performed by using the Kaplan-Meier method and multivariate Cox regression analyses; propensity score matching (PSM) analyses were performed. Thymoma data from our facilities (n = 166) were used for validation.
Results: Of 4,151 and 647 thymoma and thymic-carcinoma patients, respectively, we classified 1,618 and 268 patients into small-tumor (primary tumor size ≤ 5 cm) and large-tumor groups, respectively. Thymoma patients in the small-tumor group had a significantly longer overall survival (OS) than those in the large-tumor group (>5 cm) (median OS 193.2 vs. 161.4 months, respectively; log-rank P < 0.0001; hazard ratio 0.72; 95% confidence interval 0.64-0.82). After PSM, multivariate analysis showed that tumor size was an independent prognostic factor for OS (P < 0.0001). Validation cohort analysis supported these results. Tumor size did not have a significant impact on OS (P = 0.0994) in thymic-carcinoma patients.
Conclusions: Tumor size in thymoma, but not in thymic carcinoma, was an important prognostic factor in the U.S.
Keywords: National cancer database; Stage classification; Thymic carcinoma; Thymic epithelial tumor; Thymoma.
© 2024. Society of Surgical Oncology.