At low power, the lamina propria appears more 'pink'. The change is quite subtle and can be missed at first glance. The architecture of the colonic glands is unaffected.

On closer inspection, the lamina propria is infiltrated by large polygonal cells with coarsely granular cytoplasm such as displayed in the center of this image. The nuclei are small, and either centrally or eccentrically located.

The cytoplasmic granules are PAS positive and diastase resistant.

Note that the PAS highlights the goblet cells of the normal colonic crypts. The cytoplasmic granules of the tumor cells are also clearly evident.

GCT will stain positively with S-100 and NSE as the tumor cells are of Schwann cell origin. In this image, S-100 highlights the discrete area of GCT involvement.

A closer up image demonstrates that the lesional cells exhibit strong diffuse staining with S-100.

Granular cell tumors (GCT) are benign neoplasms that can occur in virtually every tissue and organ. 30-50% of GCT occur in the head and neck region, with the most common site being the tongue. Other sites include the GI tract, where the esophagus and large intestine are the common frequently affected.1,2

The neoplastic cells are believed to be Schwannian in origin, which is supported by IHC studies that demonstrate positivity for S-100 and NSE (neuron-specific enolase). Additionally, the granules within the tumor cells are PAS-positive and diastase-resistant.

Grossly, the tumors are yellow-gray-white nodules between 1-4 cm in diameter, arising in the submucosa or muscularis propria. The overlying mucosa is usually intact. Microscopically, the granular cells have abundant coarsely granular cytoplasm with small nuclei. The cells are bland and monomorphic. If pleomorphism, mitoses and necrosis is seen, one must consider the very rare diagnosis of a GCT with malignant potential.

Presentation depends on the location and size of the tumor. Many are discovered incidentally. In the esophagus, patients may present with dysphagia. Intestinal lesions may cause bleeding and be seen as a mass on colonoscopy.

GCT occurs over a wide age range; peak incidence is between 40-50 years of age. There is a female preponderance (2:1) and interestingly, 2/3 of patients are black. Some tumors develop following radiation therapy.2

Excellent; only 2-8% recur even after incomplete excision.1 Note that there is a very rare subset of GCT with malignant potential (~2% of GCT).3 Although no established criteria current exist, increased mitotic activity, necrosis and pleomorphism may suggest a more aggressive tumor.