Mast cell-rich leiomyomas should not be mistaken for gastrointestinal stromal tumours

Gastrointestinal Mesenchymal Neoplasms other than Gastrointestinal Stromal Tumors: Focusing on Their Molecular Aspects

Gastrointestinal (GI) mesenchymal tumors other than gastrointestinal stromal tumor (GIST) are rare neoplasms, but they often enter the differential diagnosis of more common GI lesions. Some of these mesenchymal tumors in the GI tract have well understood molecular pathologic aspects, including desmoid tumors, inflammatory myofibroblastic tumor (IMT), clear cell sarcoma (CCS), inflammatory fibroid polyp (IFP), and synovial sarcoma (SS). Molecular pathology is fast becoming a mainstream focus in laboratories because it aids in the precise classification of tumors, may be prognostic, and may help predict response to therapy. The following review is not intended as an exhaustive summary of all mesenchymal tumors that have been reported to involve the GI tract, but instead will highlight the current knowledge of the most important non-GIST GI mesenchymal neoplasms, focusing on those tumors with well-characterized molecular pathology and how the molecular pathologic features impact current diagnostic, therapeutic, and prognostic standards.

Specificity of DOG1 (K9 clone) and protein kinase C theta (clone 27) as immunohistochemical markers of gastrointestinal stromal tumour

AIMS

DOG1 and protein kinase C (PKC) theta are both sensitive immunohistochemical markers of gastrointestinal stromal tumour (GIST). However, there are conflicting data regarding the specificity of the most commonly used PKC theta antibody (clone 27), and there are no existing data regarding the specificity of the only known commercially available DOG1 antibody (K9 clone) at the time of writing. This study's aim was to characterize the immunoreactivity patterns of both monoclonal antibodies amongst a wide range of neoplasm types including, in particular, histological mimics of GIST.

METHODS AND RESULTS

Immunohistochemistry for DOG1 and PKC theta was performed on whole tissue sections from 23 different neoplasm types (total of 125 cases). Ten of these neoplasm types showed CD117 immunopositivity. Only three (Ewing's sarcoma, glomus tumour and synovial sarcoma) of the 23 neoplasm types showed DOG1 immunopositivity, and such positivity was often focal and weak in intensity. In contrast, all but four (ganglioneuromas, leiomyomas, desmoplastic small round cell tumours and PEComa/angiomyolipomas) of the 23 neoplasm types showed PKC theta immunopositivity.

CONCLUSIONS

Compared with CD117, DOG1 (using the K9 antibody) is a more specific marker, whereas PKC theta (using the clone 27 antibody) is a considerably less specific immunohistochemical marker for GIST.