Usefulness of [18F]fluoro-2-deoxy-D-glucose Positron Emission Tomography for Predicting the World Health Organization Malignancy Grade of Thymic Epithelial Tumors

Objective: The objective of this study was to investigate whether the maximum standardized uptake value (SUVmax) determined using positron emission tomography with [(18)F]fluoro-2-deoxy-D-glucose ((18)FDG-PET) can predict the grade of malignancy of thymic epithelial tumors based on the World Health Organization (WHO) classification.

Methods: We retrospectively analyzed 13 patients with thymic epithelial tumors, who underwent (18)FDG-PET examination before treatment. The patients were subdivided into a thymoma group and a thymic carcinoma group, and the two were compared clinicopathologically.

Results: There were six men and seven women, ranging in age from 36 to 78 years (mean, 58.8 ± 13.3 years). Mean tumor size was 47.3 ± 26.0mm, and the WHO classification was type A in two patients, type AB in none, type B1 in one, type B2 in three, type B3 in two, and thymic carcinoma in five. Thus, eight patients had thymoma and five had thymic carcinoma. The Masaoka stage was I in four patients, II in four, III in three, and IV in two. Mean pre-treatment SUVmax for the tumors overall was 5.24 ± 3.10, with a range of 1.73-11.21. Mean SUVmax in the thymic carcinoma group was 8.15 ± 7.88, and that in the thymoma group was 3.43 ± 2.19, the difference being significant (P = 0.002).

Conclusions: A significant relationship was observed between SUVmax and morphological classification by the WHO system for this cohort of thymic epithelial tumors. Pre-treatment SUVmax may be useful for differentiating thymoma from thymic carcinoma.