Answer: Glomus tumor

Histology: The tumor is composed of nodules of rounded cells with a hyalinized and fibrotic stroma. Cells have uniform round nuclei and well developed cytoplasm. The tumor cells label for smooth muscle actin, and label for type 4 collagen in a pericellular pattern. CD117 and desmin were negative.

Discussion: Paraganglioma would have a more vascularized stroma, and the nuclei would show more “endocrine” features in the form of finely dispersed, “salt and pepper” type chromatin. Gastric carcinoid tumors often arise is association with either atrophic gastritis or Zollinger-Ellison syndrome. Solitary gastric carcinoids can be large like the current lesion. However, they also should have more neuroendocrine type chromatin, and more trabecular patterns of growth. Epithelioid gastrointestinal stromal tumor is a serious concern in this case, particularly given that it is potentially treatable with gleevec. However, gastrointestinal stromal tumor (GIST) as defined by c-kit immunoreactivity, and the current lesion was nonreactive for c-kit (CD117).

The stomach is in fact the most common site for glomus tumor within the gastrointestinal tract. Glomus tumors are typically immunoreactive for actin, calponin, caldesmon, but negative for desmin and c-kit. The tumor has overall a favorable prognosis, even though it is deep and must be regarded as having uncertain malignant potential at the time of diagnosis.

Reference(s):
Am J Surg Path 2002;16:301-311.