Cytokeratin Positive Cystic Epithelioid Gastrointestinal Stromal Tumor Mimicking Gastric Carcinoma- Immunohistochemical Analysis and Review of Literatures.

Gastrointestinal stromal tumor is biologically heterogeneous in both morphological appearance and clinical behavior. Immunohistochemical analysis and literature review was done to explore the necessity of mutation study. We present a case study of a 40 year old male presented with upper abdominal lump, exploratory laprotomy done and a large cystic mass involving transverse colon, omentum, stomach along with gross hemoperitoneum was found. Ruptured large cystic tumor mass measuring 19X16 cms was received for histopathological examination. Grossely the cystic mass show variegated outer nodular surface with attached piece of stomach and a segment of colon. Bright field microscopy show striking perivascular arrangement of tumor cells and geographical necrosis and the report signed out as undifferentiated carcinoma stomach. Battery of immunohistochemical markers was done. Tumor cells displayed diffuse positivity for CD117, DOG1, and pan-CK along with more than focal positivity for CD34 and negative for SMA, desmin, S-100, synaptophysin, chromogranin, Bcl-2, Ki- 67. Tumor turned out to be Cytokeratin positive epithelioid gastric GIST. Cytokeratins may be expressed in high grade GISTs rarely and CK positive GISTs must be differentiated from carcinomas, melanomas and a range of CK- positive sarcomas. A panel of immunohistochemistry markers is required for diagnosis and prognostication of the tumor.