Different View on Tumor Size Dilemma in Tumor-Node-Metastasis Staging System for Thymoma

The International Association for the Study of Lung Cancer Thymic Epithelial Tumor Staging Project: Proposal for the T Component for the Forthcoming (Ninth) Edition of the TNM Classification of Malignant Tumors

INTRODUCTION

A TNM-based stage classification system of thymic epithelial tumors was adopted for the eighth edition of the stage classification of malignant tumors. The Thymic Domain of the Staging and Prognostics Factor Committee of the International Association for the Study of Lung Cancer developed a new database with the purpose to make proposals for the ninth edition stage classification system. This article outlines the proposed definitions for the T categories for the ninth edition TNM stage classification of thymic malignancies.

METHODS

A worldwide collective database of 11,347 patients with thymic epithelial tumors was assembled. Analysis was performed on 9147 patients with available survival data. Overall survival, freedom-from-recurrence, and cumulative incidence of recurrence were used as outcome measures. Analysis was performed separately for thymomas, thymic carcinomas, and neuroendocrine thymic tumors.

RESULTS

Proposals for the T categories include the following: T1 category is divided into T1a (≤5 cm) and T1b (>5 cm), irrespective of mediastinal pleura invasion; T2 includes direct invasion of the pericardium, lung, or phrenic nerve; T3 denotes direct invasion of the brachiocephalic vein, superior vena cava, chest wall, or extrapericardial pulmonary arteries and veins; and T4 category remains the same as in the eighth edition classification, involving direct invasion of the aorta and arch vessels, intrapericardial pulmonary arteries and veins, myocardium, trachea, or esophagus.

CONCLUSIONS

The proposed T categories for the ninth edition of the TNM classification provide good discrimination in outcome for the T component of the TNM-based stage system of thymic epithelial tumors.

The International Association for the Study of Lung Cancer Thymic Epithelial Tumors Staging Project: Proposal for a Stage Classification for the Forthcoming (Ninth) Edition of the TNM Classification of Malignant Tumors

INTRODUCTION

A TNM-based system for all types of thymic epithelial tumors was introduced in the eighth edition of the TNM classification of thoracic malignancies. The Thymic Domain of the Staging and Prognostic Factors Committee of the International Association for the Study of Lung Cancer, composed of multispecialty international experts, was charged to develop proposals for the ninth edition. This article outlines the proposed definitions for the T, the N, and the M components and their combination into stage groups.

METHODS

A large central database of 11,347 patients with thymic epithelial tumors was assembled thanks to the contribution of the major thymic organizations worldwide and analyses were carried out for the T, the N, and the M components and the stage groups. Overall survival was the outcome measure for patients with completely and incompletely resected tumors, and recurrence for those with complete resection. When the number of patients was sufficient, analyses were performed separately for thymomas, thymic carcinomas, and neuroendocrine thymic tumors.

RESULTS

Tumor size is included in the T1 category as T1a (≤5cm) and T1b (>5 cm); the mediastinal pleura is dropped as a T descriptor; invasion of the lung or phrenic nerve is reclassified as T2 (instead of T3). No changes are proposed for the N and the M components from the eighth edition. The stage groups remain the same.

CONCLUSIONS

The proposed changes for the ninth edition of the TNM classification set the stage for further progress in the future for these rare tumors.

Unsolved Issues in Thymic Epithelial Tumour Stage Classification: The Role of Tumour Dimension

According to the different classifications now in use, thymic tumours are staged by the extent of local invasiveness, and tumour size is not included as a major determinant for the T category. The aim of this double-site retrospective study is to analyse the correlation between tumour dimension and overall survival (OS) in patients who underwent surgical treatment. From January 2000 to December 2020, patients with thymic epithelial tumours who underwent surgical resection were included in this study. Data from a total of 332 patients were analysed. Five- and ten-year overall survival (5-10 YOS) was 89.26% and 87.08%, respectively, while five- and ten-year disease-free survival (DFS) was 88.12% and 84.2%, respectively. Univariate analysis showed a significant correlation between male sex (p-value 0.02), older age (p-value < 0.01), absence of myasthenia gravis (p-value < 0.01), increase in pTNM (pathological Tumor Node Metastasis) (p-value 0.03) and increase in the number of infiltrated organs (p-value 0.02) with an increase in tumour dimension. Tumour dimension alone was not effective in the prediction of DFS and OS, both when considered as a continuous variable and when considered with a cut-off of 3 and 5 cm. However, with multivariate analysis, it was effective in predicting OS in the aforementioned conditions (p-value < 0.01). Moreover, multivariate analysis was also used in the thymoma and Masaoka I subgroups. In our experience, the role of tumour dimension as a descriptor of the T parameter of the TNM (Tumor Node Metastasis) staging system seemed to be useful in improving this system.

Real-world study of treatment and outcome of type B2 + B3 thymoma: The neglected part of thymoma

BACKGROUND

This study aimed to examine the treatment and prognosis of patients with type B2 + B3 thymoma and compare it with those patients with type B2 and B3 thymoma.

METHODS

We conducted a retrospective analysis of the results of 39 patients with type B2 + B3 thymoma, 133 patients with type B2 thymoma, and 64 patients with type B3 thymoma. The Kaplan-Meier technique was used to generate survival curves. For multivariate analysis, the Cox proportional hazard model was applied.

RESULTS

With a median follow-up of 60 months (range: 1-128 months), the percentage of patients with tumor, node, metastasis (TNM) stage III and IV disease gradually increased from 19.5% to 25.6% to 35.9% among those with histological subtypes B2, B2 + B3, and B3, respectively, p = 0.045. Twenty-three patients experienced recurrence or metastasis. The total 10-year progression-free survival (PFS) rates were 86.0% overall (85.0% in type B2, 87.2% in type B2 + B3, and 87.5% in type B3). Age, R0 resection, and Masaoka-Koga stage were found to have a significant on PFS in all patients. There was no statistically significant difference in PFS between different histotypes of thymoma, p = 0.650. PFS was predicted by R0 resection in all histotypes and by the Masaoka-Koga stage in the type B2 subgroup.

CONCLUSION

Combining the two staging methods to guide the diagnosis and treatment of patients with B2 + B3 thymoma is recommended. R0 resection is recommended to reduce recurrence. Patients with B2 + B3 thymoma have a prognosis similar to those with a B2 thymoma or a B3 thymoma alone.

Thymic Epithelial Tumors: An Evolving Field

Despite their rarity, thymic epithelial tumors (TETs) have attracted much interest over the years, leading to an impressive number of histological and staging classifications. At present, TETs are divided by the WHO classification into four main subtypes: type A, type AB, and type B thymomas (subdivided into B1, B2, and B3), and thymic carcinomas, going from the more indolent to the most aggressive ones. Among many debated staging proposals, the TNM and the Masaoka-Koga staging systems have been widely accepted and used in routine practice. The four-tiered histological classification is symmetrically mirrored by the molecular subgrouping of TETs, which identifies an A-like and an AB-like cluster, with frequent GTF2I and HRAS mutations; an intermediate B-like cluster, with a T-cell signaling profile; and a carcinoma-like cluster comprising thymic carcinomas with frequent CDKN2A and TP53 alterations and a high tumor molecular burden. Molecular investigations have opened the way to tailored therapies, such as tyrosine kinase inhibitors targeting KIT, mTOR, and VEGFR, and immune-checkpoints that have been adopted as second-line systemic treatments. In this review, we discuss the crucial events that led to the current understanding of TETs, while disclosing the next steps in this intriguing field.

Does size affect the prognosis of resectable thymoma beyond the eighth edition TNM?

Background

Thymoma is a type of rare mediastinal tumor whose clinical characteristics and indicators of prognosis are poorly understood. This single‐institution retrospective study aimed to assess the predictive value of tumor, node, metastasis (TNM) staging incorporating tumor size in predicting the risk of thymoma recurrence after resection.

Methods

Four binary logistic regression models were developed. Models I and II included median tumor size and TNM stage, respectively. Model III included the above two variables. Model IV was model III containing these two variables and their interaction terms. All models were adjusted for WHO histological type, operational time, and adjuvant therapy.

Results

A total of 276 patients with a median age of 51.0, including 21 patients with thymoma recurrence, were included in this study. Models II or III showed a lower ‐2LogL and higher AUC (0.735 and 0.738 vs. 0.576) with significantly better discrimination than model I, and model III and model II shared similar discrimination. In model III, TNM stage was positively correlated with thymoma recurrence. The recurrence risk of patients with TNM stage IV was significantly higher than those with TNM stage I (OR of 11.03, p = 0.022). No significant correlation between the tumor size and recurrence risk (p = 0.779) and no interaction was found between medium tumor size and TNM stage in model IV.

Conclusions

This study suggests that the prediction contribution of the TNM stage combined with tumor size is similar to the TNM stage alone for tumor recurrence in patients with thymoma after surgical resection.