Histopathologic challenges: The second OPINION issue.

Classification and definition criteria for rare cancer is still an open issue in clinical practice due to several factors, which include the limited available molecular data to better defining specific tumor groups or "families" of interest. An important issue related to the proper management of these entities is the correct diagnosis and subtyping of a given entity. The high complexity associated with the histopathologic diagnosis and eventual molecular analysis may suggest the use of a histopathologic second opinion from a specialized pathologist. Diagnostic inaccuracies and difference between primary diagnosis and second opinion are expected at the population level: however, the magnitude of this difference is remarkably high and calls for implementation of second opinion in routine practice outside reference centers.