Classification and Diagnostics
There are no guidelines for the diagnosis and treatment of the overall rare mediastinal tumors. The classification of thymomas is based on the repeatedly revised WHO classification and the Masaoka-Koga classification, which is commonly used in clinical practice and evaluates based on infiltration and capsular invasion. In the WHO classification, types are categorized by histology from Type A (most benign behavior) to Type C (most aggressive behavior).
Masaoka-Koga Classification
Stage I | The tumor is still confined to the thymus gland and the thymic capsule—it has not yet penetrated them. |
Stage IIa | The tumor has only slightly penetrated the capsule. |
Stage IIb | The tumor has left the thymus gland and spread to surrounding fatty tissue up to the pleura. It is adherent to the pleura or pericardium. |
Stage III | The tumor has invaded neighboring organs, such as the pericardium, lungs, large vessels, or certain nerves. |
Stage IVa | The tumor has spread in the heart or lung pleura. |
Stage IVb | Cancer cells have spread through the bloodstream and lymphatic pathways to other organs—distant metastases form. |
For the diagnosis of mediastinal tumors, in addition to thoracic computed tomography, magnetic resonance imaging is a valuable supplement, especially in advanced cases, to improve the assessment of operability. The extent to which a nuclear medicine examination using DOTATOC-PET/CT should be performed for each patient is still under discussion.
Therapy
The gold standard of therapy for surgically completely resectable thymomas is surgery and R0 resection as the most important prognostic factor. In initially inoperable patients, resectability and thus a good prognosis can be achieved through neoadjuvant therapy after appropriate case discussion in tumor boards. (1, 2) A radical lymph node dissection only contributes to improved survival in thymic carcinomas.
For a long time, sternotomy was recommended as the standard approach for reasons of surgical radicality. (3) Initially, minimally invasive surgery was only performed on very small thymomas under 4cm. However, through growing experience in video-assisted surgery and the possibilities of robotic surgery, oncological equivalence for thymomas in Stage I and II has been demonstrated in some studies. (4, 5)
Prognosis
Statistically, thymomas have a relatively high local recurrence rate of up to 10% after surgical removal, which is why adequate and close follow-up is recommended. While the 5-year survival rate for thymomas of Type A (according to WHO) is 100% and Type B (according to WHO) is 93%, it drops to 23% for thymic carcinomas of Type C (according to WHO).