Historical perspectives: The evolution of the thymic epithelial tumors staging system.

Thymic epithelial tumors (thymomas, thymic carcinomas and neuroendocrine tumors - NETs) are rare primary mediastinal neoplasms, recently classified as orphan diseases. Their rarity might explain the fact that currently, no official staging system has been defined by the Union Internationale Contre le Cancer (UICC) and the American Joint Commission on Cancer (AJCC). However, the appropriate staging of these tumors has been matter of debate and several proposals have been published over the years, but very few have received a clinical validation. Recently an international database for thymic malignancies has been provided by the International Thymic Malignancy Interest Group (ITMIG); one of its aims is to accomplish a new and evidence based staging system, to allow progress in clinical management in thymic tumors. This paper will review the history of proposed staging systems, comparing resemblances and differences, being a sort of starting point for the development of a new widely accepted clinical staging system.