P23: Tumor volume of thymic epithelial tumors based on who histological classification

Background: Our aim was to assess the tumor volume for various subtypes of thymic epithelial tumors based on the World Health Organization classification.

Methods: We retrospectively reviewed CT scans of 64 patients with thymic epithelial tumors pathologically proven by thymectomy or biopsy performed at our institution between January 2010 and December 2013. Forty-seven patients (two patients with type A, 13 with type AB, 14 with type B1, 12 with type B2, six with type B3), and 17 with thymic carcinomas were included. Tumor volumes were automatically calculated using a modified commercially available software [M.Y.1] (LISIT, Co., Ltd). We analyzed the correlation of the tumor volume and histological subtypes according to the World Health Organization classification using Mann-Whitney U test and Scheffe’s F test.

Results: The measured tumor volumes ranged 0.502–46.9 cm³ (mean ± SD: 64.9±94.6). The tumor volumes (mean ± SD) in each WHO histologic type were 127.1±74.5 cm³ in type A; 39.0±35.1 cm³ in type AB; 51.6±104.6 cm³ in type B1; 45.1±52.0 cm³ in type B2; and 29.5±22.7 cm³ in type B3 tumors, respectively. The tumor volumes (mean ± SD) in thymic carcinoma were 114.7±129.2 cm³. There was no statistical significant difference in the volume of thymic epithelial tumors among each WHO histologic type or between low risk thymoma and high risk thymoma (all comparison, P>0.05). Significant advantages for differentiating tumors were observed between thymomas and thymic carcinomas in the tumor volume. Thymic carcinomas were significantly larger than thymomas (P=0.0080).

Conclusions: Thymic carcinoma tends to show larger tumor volumes than thymoma at the time of initial presentation. However, tumor volume may not be useful to differentiate among thymomas of each histological subtype.

Keywords: WHO histological classification; tumor volume; thymic epithelial tumor