AB018. Superior mediastinal tumor, distribution of the diseases, and its clinical course

Background: Thymomas originating from the superior mediastinum (cephalad to the left brachiocephalic vein) are relatively rare and reported to have a poorer prognosis. The four-compartment classification model, which includes the superior portion of the mediastinum, has the advantages of “sufficient separation of disease distribution” and “differentiation of prognosis of thymic epithelial tumors (TETs) by tumor location”. We aimed to validate these advantages using our clinical data.

Methods: We retrospectively reviewed the patients who underwent therapeutic resection of anterior/superior mediastinum tumors at Nishi-Kobe Medical Center from 1 January 2017 to 31 March 2024. We evaluated the location of the tumors, the surgical procedure, the clinicopathological features, and the patients’ survival outcomes. The compartment’s boundaries were defined according to the Japanese Association for Research on the Thymus (JART) general rules.

Results: A total of 84 patients were eligible for this study. Thyroid tumors (superior 3: anterior 0, P=0.002) and schwannomas (2:0, P=0.02) were specific to the superior mediastinum group (n=11), compared with the anterior mediastinum group (n=73). Meanwhile, the proportion of TETs (Sup 3: Ant 39, P=0.19) and cysts (3:28, P=0.74) were not distinctive. In the TETs group (n=42), the breakdown of diseases [thymoma with myasthenia gravis (MG), Sup 0: Ant 12; thymoma without MG, 2:13; thymic cancer, 1:4] was not different by the location. The open procedures were common (Sup, median sternotomy: trans-manubrial: thoracoscopic =1:1:1; Ant, 10:0:29, P=0.048), R1 resection was frequent (Sup: 66%; Ant: 10%, P=0.09), and the prognosis was poorer (2-year disease-free survival, Sup, 0.5; Ant, 0.927, P=0.007) in superior mediastinum group, whereas the tumor size (Sup, 46.7 mm; Ant, 48.9 mm, P=0.88), and pT factor (Sup, T1:T2:T3 =2:0:1; Ant, 31:3:3, P=0.45) were similar.

Conclusions: While International Thymic Malignancy Interest Group (ITMIG) classification of mediastinal compartment did not distinguish superior mediastinum, the four-compartment classification proposed by JART which includes a superior portion, was useful in recalling the specific disease (thyroid tumor, etc.) and supposing the difficulty of resection or the prognosis of TETs.

Keywords: Superior mediastinum; Japanese Association for Research on the Thymus (JART); four-compartment classification