Introduction

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract and originate from the interstitial cells of Cajal. They usually display spindle cell or epithelioid morphology and characteristically express KIT (CD117) and/or DOG1. Unusual histological patterns, including schwannian-like features, may be encountered and represent a diagnostic challenge, particularly in gastric tumors.

Methods

We report a clinicopathological study of a surgically resected gastric mass in a 64-year-old patient. Gross examination and routine histological analysis using hematoxylin and eosin staining were performed. Mitotic activity was assessed in high-power fields. Immunohistochemical studies included DOG1, CD117, CD34, S100 protein, desmin, and smooth muscle actin (SMA).

Results

The tumor arose from the greater curvature of the stomach and measured 21 cm in greatest dimension. Histologically, the lesion was ulcerated at the surface and composed of spindle cells arranged in a nodular architecture, with nodules separated by fibrous septa. Tumor cells showed nuclear palisading, creating a schwannian-like appearance. The stroma was predominantly fibrous with focal myxoid areas, and tumor necrosis was present. A high mitotic rate was identified, estimated at 25 mitoses per 21 high-power fields. Immunohistochemically, the tumor cells showed diffuse positivity for DOG1, CD117, and CD34, while S100 protein, desmin, and smooth muscle actin were negative.

Conclusions

This case highlights a giant gastric GIST with schwannian-like features that may closely mimic a gastric schwannoma. Recognition of this morphological pitfall is crucial to avoid misdiagnosis. Immunohistochemistry remains indispensable for accurate diagnosis and prognostic assessment.