Based on the histological features and outcome, the current WHO classification separates
thymomas into A, AB, B1, B2 and B3 subtypes. It is hypothesized that the type A
thymomas are derived from the thymic medulla while the type B
thymomas are derived from the cortex. Due to occasional histological overlap between the
tumor subtypes creating difficulties in their separation, the aim of this study was to provide their proteomic characterization and identify potential immunohistochemical markers aiding in tissue diagnosis. Pair-wise comparison of neoplastic and normal thymus by liquid chromatography tandem mass spectrometry (LC-MS/MS) of
formalin fixed
paraffin embedded tissue revealed 61
proteins differentially expressed in
thymomas compared to normal tissue. Hierarchical clustering showed distinct segregation of subtypes AB, B1 and B2 from that of A and B3. Most notably, desmoyokin, a
protein that is encoded by the AHNAK gene, was associated with type A
thymomas and medulla of normal thymus, by LC-MS/MS and immunohistochemistry. In this global proteomic characterization of the
thymoma, several
proteins unique to different thymic compartments and
thymoma subtypes were identified. Among differentially expressed
proteins, desmoyokin is a marker specific for thymic medulla and is potentially promising immunohistochemical marker in separation of type A and B3
thymomas.