Thymoma versus thymic carcinoma: differences in biology impacting treatment.

A better understanding of the biology of both thymomas and thymic carcinomas has occurred in recent years thanks to advanced technologies such as comparative genomic hybridization, expression array analysis, and next-generation sequencing. Gene expression profiling and genomic clustering studies have shown that thymic tumors as classified by the 2004 WHO system do have different molecular features. Because of the rarity of these tumors, there is a paucity of high-quality clinical research data, and treatment decisions are often guided by the small amount of prospective trial data, retrospective series, and individual case reports. The literature does report on several advanced thymic tumors that have responded to new targeted agents, indicating that across the spectrum of thymic malignancies there may be clinically relevant molecular subsets. Genomic profiling distinguishes type B3 thymoma and thymic carcinoma from type A and B2 thymomas. Furthermore, type B2 thymomas can be separated from other subgroups in that it has a more distinctly lymphocytic component than the other groups in which epithelial cells predominate. The presence of KIT mutations in thymic carcinomas rather than in thymomas further adds to a growing body of evidence showing that underlying tumor biology may in the future lead to molecular classifications, which may enhance therapies for these rare tumors.