AB018. Advances in mediastinal tumors diagnosis: J. Rosai, a master of Pathology, and the value of morphology and related disciplines

Background: In the last 60 years, significant progresses were made in diagnostics of mediastinal tumors from the confusing existing situation. Finally, with the immunological discovers concerning thymic functions, a new era began due to the excellent diagnostic skill of Juan Rosai. He was born in Italy, Poppi, in 1940. Emigrated to Argentina with the family, after his degree in Medicine and training in pathology, J. Rosai was invited to join United States and in short, he was very well appreciated in the group of Lauren Ackerman. He was Professor and Chairman of Pathology in several University, in United States and Director of the Pathology Department at the National Cancer Institute in Milan, Italy. His excellent morphologic skill, comprehensive understanding of diagnostic patterns and exceptional memory rendered him a Master in pathology and in Surgical Pathology.

Methods: J. Rosai based his experience and skills on the examination of series of hundreds of cases from the Armed forces Institute of Pathology, from many other Institutions and consultation cases. To the morphological observations with H&E stained cases, he added electron microscopic studies and later on he was a master in immunohistochemistry interpretation in the correct contexts.

Results: Several mediastinal tumor entities were first diagnosed and characterized. Thymic epithelial tumors (TET) were clearly described for their epithelial nature, independently from the lymphocytic content; prognostic factors were defined. The 1999 WHO classification of TETs was proposed, as a result of long debate among Pathologist from all the world, and is now widely diffused. He was participating to the early steps of ITMIG establishment. Before the 2015 WHO classification, he also participated to the improvements and discussions related to the classification, in order to refine the diagnostic criteria and improve the reproducibility of TET diagnosis.

Conclusions: J. Rosai was a master in surgical pathology and in teaching it. He understood the added value of emerging new techniques supporting the pathological diagnoses. In mediastinal pathology he contributed together and perhaps more than other masters in clarifying the histogenesis of specific diseases and tumors.

Keywords: Mediastinum; thymic epithelial tumors (TETs); pathology; diagnosis