4) The thymoma was completely encapsulated without microscopic or macroscopic invasion of the surrounding capsule, tissue, or vessels, so that according to the Masaoka staging
system, which is used widely in human medicine, a benign stage was diagnosed.
In 1994, Koga et al (33) modified the Masaoka staging, changing invasion into the tumor capsule (Masaoka stage II/2) to microscopic invasion through the capsule (transcapsular; Koga stage IIA) to accommodate the most common point of view of pathologists that a tumor is invasive if it grows through the tumor capsule (Table 6).
In 1991, Yamakawa and colleagues (36) proposed a tentative tumor-node-metastasis (TNM) classification that was similar to the Masaoka staging system but distinguished between lymphogenous and hematogenous metastases (Table 6).
The modified Masaoka staging system (Masaoka-Koga staging system) appears to be the most commonly used staging system for thymomas, whereas the TNM staging as recommended by the WHO (Table 6) might be used for thymic carcinoma.
Table 1: World Health Organization classification of thymoma Type Histologic description A Medullary thymoma AB Mixed thymoma B1 Predominantly cortical thymoma B2 Cortical thymoma B3 Well-differentiated thymic carcinoma C Thymic carcinoma Table 2: Masaoka staging
system of thymoma Stage 1 Encapsulated tumor with no gross or microscopic invasion Stage 2 Macroscopic invasion into mediastinal fat or pleura Stage 3 Invasion of pericardium, great vessels, or lung Stage 4 Pleural or pericardial metastatic spread Stage 5 Lymphatic or hematogenous spread
In this study, the Masaoka staging system of thymoma was used for the classification of thymic neoplasms.
Thymoma: interrelationships among World Health Organization histology, Masaoka staging and myasthenia gravis and their independent prognostic significance: a single-centre experience.
We have discussed the various histological classifications for thymomas as well as the widely accepted postsurgical Masaoka staging
, which is an independent predictor of outcome and survival.
Prognosis is now based on a number of variables, mainly Masaoka staging, the WHO histologic subtype (A, AB, B1, B2, B3, and C), and other factors, such as completeness of surgical resection, pleural involvement, and the diameter of the tumor.
Results of surgical resection for patients with thymoma according to World Health Organization histology and Masaoka staging.
This was done because Masaoka staging alone can miss the true oncologic implications of thymoma; in fact, recurrence may appear in a fairly great percentage of patients with early stage thymoma.
Do they agree with our words of caution about considering the Masaoka staging system as the only predictive variable?