Introduction

Pathologists are staging thymic epithelial tumors (TET) according to the 8th UICC/AJCC TNM system. Within the French RYTHMIC network, dedicated to TET, agreement on pathologic tumor stage (pT) among the pathology panelists was difficult. The aim of our study was to determine the interobserver reproducibility of pT at an international level, to explore the source of discrepancies and potential interventions to address these.

Methods

An international panel of pathologists was recruited through the International Thymic Malignancy Interest Group (ITMIG). The study focused on invasion of mediastinal pleura, pericardium, and lung. From a cohort of cases identified as challenging within the RYTHMIC network, we chose a series of test and validation cases (n = 5 and 10, respectively).

Results

Reproducibility of the pT stage was also challenging at an international level as none of the 15 cases was classified as the same pT stage by all ITMIG pathologists. The agreement rose from slight (κ = 0.13) to moderate (κ = 0.48) between test and validation series. Discussion among the expert pathologists pinpointed two major reasons underlying discrepancies: 1) Thymomas growing with their “capsule” and adhering to the pleurae, pericardium, or lung were often misinterpreted as invading these structures. 2) Recognition of the mediastinal pleura was identified as challenging.

Conclusion

Our study underlines that the evaluation of the pT stage of TET is problematic and needs to be addressed in more detail in an upcoming TNM classification. The publication of histopathologic images of landmarks, including ancillary tests could improve reproducibility for future TNM classifications.

中文翻译：

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胸腺上皮肿瘤分期的国际可重复性研究：pT 分期是一个问题。改进建议。 RYTHMIC/ITMIG 研究

介绍

病理学家正在根据第 8 版 UICC/AJCC TNM 系统对胸腺上皮肿瘤 (TET) 进行分期。在致力于 TET 的法国 RYTHMIC 网络中，病理小组成员很难就病理肿瘤分期 (pT) 达成一致。我们研究的目的是确定国际水平上 pT 观察者间的可重复性，探索差异的根源以及解决这些问题的潜在干预措施。

方法

通过国际胸腺恶性肿瘤兴趣小组 (ITMIG) 招募了一个国际病理学家小组。该研究的重点是纵隔胸膜、心包和肺的侵犯。从 RYTHMIC 网络中被确定为具有挑战性的一组案例中，我们选择了一系列测试和验证案例（分别为 n = 5 和 10）。

结果

pT 分期的可重复性在国际水平上也具有挑战性，因为所有 ITMIG 病理学家均未将 15 例病例归类为相同的 pT 分期。测试系列和验证系列之间的一致性从轻微 (κ = 0.13) 上升到中等 (κ = 0.48)。病理学家专家之间的讨论指出了造成差异的两个主要原因：1）胸腺瘤与其“包膜”一起生长并粘附在胸膜、心包或肺上，常常被误解为侵入这些结构。 2）纵隔胸膜的识别被认为具有挑战性。

结论

我们的研究强调，TET pT 阶段的评估存在问题，需要在即将推出的 TNM 分类中更详细地解决。标志性组织病理学图像（包括辅助测试）的发布可以提高未来 TNM 分类的可重复性。