Masaoka-Koga and TNM Staging System in Thymic Epithelial Tumors: Prognostic Comparison and the Role of the Number of Involved Structures.

Background: The aim of this study was to evaluate the Masaoka-Koga and the tumor node metastases (TNM) staging system in thymic epithelial tumors (TET) considering possible improvements.

Methods: We reviewed the data of 379 patients who underwent surgical resection for TET from 1 January 1985 to 1 January 2018, collecting and classifying the pathological report according to the Masaoka-Koga and the TMN system. The number of involved organs was also considered as a possible prognostic factor and integrated in the two staging systems to verify its impact.

Results: Considering the Masaoka-Koga system, 5- and 10-year overall survival (5-10YOS) was 96.4% and 88.9% in stage I, 95% and 89.5% in stage II and 85.4% and 72.8% in stage III ( 0.01), with overlapping in stage I and stage II curves. Considering the TNM system, 5-10YOS was 95.5% and 88.8% in T1, 84.8% and 70.7% in T2 and 88% and 76.3% in T3 ( 0.02), with overlapping T2-T3 curves. Including the number of involved structures, in Masaoka-Koga stage III, patients with singular involved organs had a 100% and 76.6% vs. 87.7% 5-10YOS, which was 76.6% in patients with multiple organ infiltration. Considering the TNM, T3 patients with singular involved structures presented a 5-10YOS of 100% vs. 62.5% and 37.5% in patients with multiple organ involvement ( 0.07).

Conclusion: The two staging systems present limitations due to overlapping curves in early Masaoka-Koga stages and in advanced T stages for TNM. The addition of the number of involved organs seems to be a promising factor for the prognosis stratification in these patients.