Classification of thymic epithelial neoplasms is still a challenge to thoracic pathologists: a reproducibility study using digital microscopy.

Context: Thymic epithelial tumors are rare, constituting interpretive challenges for pathologists. Digital imaging can be useful as an educational tool for these rare tumors.
Objectives: To evaluate the diagnostic reproducibility of thymic tumors among thoracic pathologists.
Design: Twenty cases of thymoma or thymic carcinoma were scanned into the Aperio system. The images were sent to pathologists with expertise in thoracic pathology at 6 different centers, who were asked to classify the tumors according to the 2004 World Heath Organization classification and to diagnose invasion. Interobserver agreement was evaluated. After discussion of the first 20 cases, a second set of 10 cases was evaluated.
Results: There was agreement for the diagnosis of thymoma and thymic carcinoma in 70% of cases (n = 14); in the remaining 6 cases, there was disagreement for cases of B3 thymoma (n = 5) and type A thymoma (n = 1) and thymic carcinoma. The overall κ was 0.39. When invasion was evaluated, the overall κ was 0.45. In the second round of the study, after discussion of diagnostic criteria, the interobserver agreement for the diagnosis of thymoma versus thymic carcinoma was 0.67 and that for the determination of invasion was 0.57-suggesting interpretative improvement.
Conclusion: The reproducibility of diagnosis of thymic epithelial tumors, using digital imaging, is comparable to that in previous studies using glass slides. Digital imaging is a good tool for remote consultation and for educational purposes. This technology could be used to train pathologists with low-level experience in thymic epithelial tumors and to foster collaborative work in the field.