DOG1 for the Diagnosis of Gastrointestinal Stromal Tumor (GIST): Comparison Between 2 Different Antibodies

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal neoplasm of the gastrointestinal tract. Discovered on GIST-1 (DOG1) is a recently described protein expressed in GISTs irrespective of mutation status. The aim of this study was to investigate the immunohistochemical expression of DOG1 using 2 different monoclonal antibodies (DOG1.1 and the commercially available K9 antibody) in 668 GIST cases and to compare the results with the expression of KIT. DOG1 and KIT expression also were studied in most human normal tissues and several nonmesenchymal and mesenchymal tumors other than GIST. KIT was expressed in 643 (96.3%) GISTs. DOG1.1 and K9 were positive in 538 (80.5%) and 642 (96.1%) GIST cases, respectively. In 25 (3.7%) KIT-negative GIST cases, DOG1 was expressed in 5 (20.0%) and 19 (76.0%) using DOG1.1 and K9 antibodies, respectively. Only 0.9% of GISTs were negative for KIT, DOG1.1, and K9. Most normal human tissues did not reveal KIT and DOG1 expression. DOG1.1 was positive in only 2 of 57 synovial sarcomas and 1 of 61 soft tissue leiomyosarcomas. K9 was positive in 5 of 57 synovial sarcomas, 1 of 14 angiosarcomas, 1 of 61 soft tissue leiomyosarcomas, 3 of 4 adenoid cystic carcinomas of the head and neck, and in myoepithelial cells of 9 of 11. broadenomas of the breast. In conclusion, the commercially available K9 is of great utility for the diagnosis of most KIT-negative GISTs, and the combination of both KIT and K9 antibody in a panel of immunohistochemistry can define the diagnosis of GIST in more than 99% of cases.

Gastrointestinal stromal tumor in Brazil: Clinicopathology, immunohistochemistry, and molecular genetics of 513 cases

The aim of the present study was to evaluate the clinicopathological, immunohistochemical, and molecular genetic features of gastrointestinal stromal tumors in Brazil and compare them with cases from other countries. Five hundred and thirteen cases were retrospectively analyzed. HE-stained sections and clinical information were reviewed and the immunohistochemical expression of CD117, CD34, smooth-muscle actin, S-100 protein, desmin, CD44v3 adhesion molecule, p53 protein, epidermal growth factor receptor, and Ki-67 antigen was studied using tissue microarrays. Mutation analysis of KIT and platelet-derived growth factor receptor-alpha genes was also performed. There was a slight female predominance (50.3%) and the median age at diagnosis was 59 years. The tumors were mainly located in the stomach (38.4%). Immunohistochemistry showed that CD117 was expressed in 95.7% of cases. Epidermal growth factor receptor expression was observed in 84.4% of tumors. p53 protein expression was found only in 2.6% of cases but all belonged to the high-risk group for aggressive behavior according to the National Institutes of Health consensus approach. No CD44v3 adhesion molecule expression was detected. KIT exon 11 mutations were the most frequent (62.2%). The present data confirm that gastrointestinal stromal tumors in Brazilian patients do not differ from tumors occurring in other countries.