Gastrointestinal stromal tumor (GIST), importance of macro-microscopic and immunohistochemical study to determine the risk of disease progression. About two cases

Abstract

Gastrointestinal stromal tumors (GIST) are the most frequent mesenchymal neoplasms of the gastrointestinal tract, the stomach being the most involved organ. They originate from the interstitial Cajal cells of the myenteric plexus of the muscularis propria and most present mutations in the KIT proto-oncogene (exon 11).  They usually present with abdominal pain and hemorrhage, and sometimes it is an incidental finding. In 25% of cases it has malignant behavior, but its complete resection improves the local recurrence rate and overall survival. Macroscopic and microscopic study is fundamental for its diagnosis. However, nowadays it is necessary to complement it with techniques such as immunohistochemistry (IHC) to determine both the cellular origin and to quantify the mitotic range. This is an indispensable element to evaluate the risk of progression of the disease, according to the protocol of the College of American Pathologists (CAP). The aim of this report is to present two cases of rare gastric mesenchymal tumors, undergoing surgery in the Pathology Department of Oulton Institute, which showed similar imaging, macroscopic, histopathologic and IHC characteristics.

In both cases partial gastrectomy specimens were received, with submucosal, unifocal nodular lesions, one 2 cm and the other 6.5 cm in diameter, microscopically exhibited mesenchymal cell proliferation, fused, swirling arrangement, with mitosis rate less than 5/25 CGA (high magnification fields), without necrosis and with free surgical margins. IHC profile: CD117, DOG1 and CD34 positive, S100, glial fibrillary acidic protein, smooth muscle actin and Vimentin negative. There was no risk of disease progression in the smaller tumor (0%) and LOW (3.6%) risk in the larger one.

The low frequency of these tumors makes diagnosis a great challenge. At present, in addition to the macro and microscopic study, the implementation of IHC allows us to determine the cellular origin and mitosis rate of the tumors to assess the risk of disease progression.