Doubling time of thymic epithelial tumors correlates with world health organization histopathologic classification

OBJECTIVE. Awareness of volume doubling times (VDTs) of different thymic epithelial tumors (TETs), including low-and high-grade thymomas and thymic carcinomas, is important for their management. The purpose of this study was to evaluate the VDTs of incidentally found TETs using 3D volumetry (3D-VDT) and longest diameter (LD-VDT). MATERIALS AND METHODS. This retrospective study included 50 patients (30 men, 20 women) who had histologically proven TETs and who underwent at least two serial CT studies at greater than 2-month intervals. TETs were classified into World Health Organization subtypes and further divided into low-grade (group A [A.B1]) and high-grade (group B [B2, B3]) thymoma and thymic carcinoma (group C). Tumor volumetry was performed by either manual segmentation (3D-VDT) or longest diameter measurement (LD-VDT). RESULTS. Groups A, B, and C accounted for 15, 26, and nine tumors. The median LDVDT in group A was 703.6 days (range, 286.7.1855.9 days); group B, 412.1 days (range, 130.9.716.9 days), and group C, 146.3 days (range, 68.9.448.3 days) (p < 0.01). The median 3D-VDTs were 1138.8 days (range, 350.1.3915.3 days), 711.0 days (range, 145.5.7209.5 days), and 203.1 days (range, 58.9.766.9 days) (p < 0.01). In ROC analysis, both LD-VDT (AUC, 0.873; p < 0.01; optimal cutoff value, 222.6 days; 90.2% sensitivity, 77.8% specificity) and 3DVDT (AUC, 0.859; p < 0.01; optimal cutoff value, 218.0 days; 92.7% sensitivity; 66.7% specificity) differentiated group C from groups A and B. CONCLUSION. VDTs differ among TETs according to tumor grade. Measurement of either LD-VDT or 3D-VDT is sensitive for differentiating carcinomas from thymomas (cutoff value, ≈ 220 days).