Gastrointestinal Stromal Tumor with Structures Resembling Intracytoplasmic Lumina

Abstract

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gut. It is characterized by positive immunostaining for CD117, and bears mutations in the c-kit or PDGFRA genes. Its origin remains uncertain. GISTs mainly possess primitive smooth muscle or neuronal differentiation. Although an epithelioid pattern of GIST is a common finding on light microscopy, true epithelial differentiation has never been demonstrated by either immunohistochemistry or ultrastructural study. Here the authors report an epithelioid GIST of the stomach, immunopositive for CD117, DOG1.1, CD34, and PDGFRA, with slight cytoplasmic staining for epithelial membrane antigen. One heterozygous mutation on codon 842 of exon 18 of the PDGFRA gene was also found. Ultrastructurally, tumor cells had plentiful organelles, including some membrane-bound, dense-core granules and cytoplasmic vacuoles. Intermingled thin cellular processes were also found. Unusually, there were many structures resembling glandular epithelial intracellular lumina with processes. The processes, although resembling microvilli, did not have filament cores, while the lumina were either empty or contained some dense or flocculent content of uncertain nature. True intracellular lumina are very rare in GIST and the authors present findings related to this issue, with a discussion on their nature, origin, and significance.

Gastric epithelioid gastrointestinal stromal tumor with signet ring-like cell features: A case report

“…[2] Myxoid stroma is also a finding in epithelioid GISTs. [3] These intracytoplasmic, perinuclear vacuoles have been studied with electron microscopy; some authors characterize them as true lumens or lipid-like structures, [4] and others have observed that these vacuoles are empty and uncoated, perhaps due to artifacts from the paraffin block preparation. [2] The epithelioid type is not more aggressive than other types of GIST.…”