Table of Contents
Introduction:
The Masaoka stage system for thymoma was proposed in 1981. Although many surgeons and pathologists support the Masaoka staging system, numerous revisions and enhancements have been proposed. Masaoka's four-tiered staging approach was proposed in 1981, and Koga et al. submitted a variation in 1994. This updated classification system is being used the most. When examining their definitions, many institutions and authors claim to utilize the Masaoka system.
What Is Thymoma?
Thymoma and thymic carcinomas are cancers that affect the thymus, an organ positioned between the lungs and involved in the lymphatic and immune systems. The thymus serves where T-cells grow before traveling to lymph nodes throughout the body. These T-cells play a critical role in the body's ability to adapt to and fight new illnesses caused by bacteria, viruses, and fungal infections. The thymus achieves full maturity throughout puberty. Following this stage, the organ gradually begins to be substituted with fatty tissue as the patient ages.
Previously, the medical profession believed that thymoma might be benign (noncancerous) or malignant (cancerous). Thymoma and thymic carcinoma, commonly known as thymic epithelial tumors (TETs), are uncommon malignancies that can develop in the cells lining the thymus's exterior. The thymus is a tiny organ located in the upper chest, above the heart, and below the breastbone. It is part of the lymphatic system and produces white blood cells known as lymphocytes, which aid in the fight against infection. These tumors typically develop between the lungs in the front section of the chest and are occasionally discovered by a chest X-ray for another cause.
What Is the Masaoka Staging System for Thymomas?
The Masaoka-Koga classification system focuses on the original tumor's local spread, while nodal involvement plays a minor role. This is consistent with the observation that involvement of nodes is infrequent in thymomas but not in thymic carcinomas. General criticisms of the Masoaka and Masaoka-Koga staging systems include the fact that there is little, if any, surviving difference between stages I and II and that stage III encompasses a wide range of macroscopic and microscopic involvement of the aorta, lung, and heart. An improved staging system will necessitate prospective research and careful examination. The purpose is to adhere as closely as feasible to the present stage classification while defining nuances so that prospective data is collected consistently.
Stage I:
A stage I thymoma is thought to have no transcapsular invasion. Stage I, localized thymoma, invades the capsule but does not pass through it. The tumor must break through the capsule to be classified as invasive and no longer stage I. Stage I thymoma, like cancer in situ, is not considered benign. Furthermore, all significant series with long-term follow-up have shown recurrences and metastasis of stage I thymoma of all histologic kinds. As a result, all thymomas are classified as malignant since they exhibit these characteristics.
Stage II:
A tumor with trans capsular invasion is classified as stage II. If the tumor has limited microscopic expansion into tissues surrounding the capsule (≤3 mm), it should be classified as stage IIa, which is minimally invasive. The tumor should be defined in this way if it extends beyond the capsule, whether it invades parathymic fat or the normal thymus exterior of an encapsulated thymoma.
In contrast, a simple tumor-to-tissue interface in locations without a full capsule should not be classed as invasion but rather as stage I. Only microscopically proven invasion into adjacent structures should be counted; if invasion is suspected but not microscopically proven to be present, the original suspicion should not be included in stage classification. Masaoka-Koga stage IIb cancers are severely invasive into adjacent thymic or mediastinal fatty tissue. The distance between the two should be recorded when a tumor approaches the mediastinal pleura or pericardium without invading it.
Stage III:
The Masaoka-Koga classification mentions the pericardium ambiguously at both stages IIb and III. If there is simply invasion into the fibrous layer of the pericardium, or penetration into the serosal layer or onto the serosal pericardial surface, note it in the pathology report. The mediastinal pleura is a less substantial structure. Stage III should be ascribed using the notion that microscopic findings are the final determinant rather than a gross impression not supported microscopically.
As a result, adherence to structures such as the lung, phrenic nerve, or pericardium should not be considered if there is no microscopically confirmed involvement. Microscopic penetration into the mediastinal pleura, pericardium, phrenic nerve, and so on is required to designate the tumor as stage III, even if these structures adhere to the thymus tumor.
Stage IVa:
Pleural or pericardial tumor nodules distinct from the original tumor are called stage IVa. These distinct tumor nodules can be found on the visceral or parietal pleural, pericardial, or epicardial surfaces. Stage III refers to the direct expansion of a thymic malignancy to the pericardial or pleural surface without discrete nodules.
Stage IVb:
Stage IVb involves nodes around the thymus. This contains nodes in the anterior mediastinum, paratracheal, and subcarinal regions and nodes around the thymus gland's superior poles. This stage classification should also include further mediastinum or chest nodes. Extrathoracic nodes should be considered distant metastases; this is consistent with the terminology used for other cancers. Pulmonary nodules in the lung that have a rim of normal lung between them and the pleural surface are considered distant metastases. Extrathoracic tissues should be classed as metastases.
Conclusion:
The Masaoka staging method is still a valuable and reliable prognostic factor for thymoma. However, various ideas for revising the staging method have been made to uncover substantial changes in survival rates between each indicated stage. The advancement of metastasis to lymph node stations is an important aspect of the staging system for malignancies of different organs. Lymph node metastasis is a rare occurrence in thymoma, and the stages of progression are poorly described.
