The following light microscopic images were obtained from colon specimens. The patient received a diagnosis of signet ring cell adenocarcinoma of the colon. In what organ is this condition most commonly diagnosed?
a. Colon
b. Rectum
c. Stomach
d. Bladder
e. Gallbladder
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Answer to September/October's Case of the Month
b. 85 percent of GISTs are associated with KIT mutations
Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the GI tract. Whereas 85 percent of GISTs are associated with KIT mutations, 10 percent are associated with PDGFRA mutations and a small proportion are associated with mutations in the succinate dehydrogenase (SDH), NF1, or BRAF genes.
This case show features diagnostic of gastrointestinal stromal tumor (GIST) arising from the duodenal wall. The tumor comprises fascicles and sheets of spindle cells with focal epithelioid morphology; small intestinal GISTs more commonly show skeinoid fibers. The cytological smears show bland spindle cells and few epithelioid cells. The tumor cells stain positive for c-Kit (CD117) and DOG1 by IHC; Sanger sequencing shows a KIT exon 9 mutation, making this tumor less susceptible to imatinib.
Submitted by Vishnu Chandra Kumar Annadurai, Fellowship Trainee in Molecular Pathology; Thomas Alex Kodiatte, Professor; and Rekha Pai, Professor, Christian Medical College, Vellore, India.
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