Microscopic description and IHC:

The histologic sections show sheets of tumor cells predominantly within the submucosa, and on some sections they appear to arise from muscularis propria. They show a combined spindled (not shown) and epithelioid morphology, with focal hypercellular areas showing rhabdoid and signet ring cell features (best seen in photographed sections).

The tumor cells were positive for CD117 and DOG1, and negative for S-100, Melan-A, SMA, CDX2, and mucicarmine.

Discussion:

Gastrointestinal stromal tumors, or GISTs, as the name would imply, are predominantly found in the gastrointestinal system, although a minority can be found outside the GI tract (omentum, prostate, retroperitoneum, pelvic organs) (1). Moreover, approximately 85% of sarcomas found in the GI tract are GISTs. They are most commonly seen in the stomach and arise from the interstitial cells of Cajal and usually metastasize to the liver and peritoneum.

About 20-25% of GISTs are categorized as malignant. To characterize a GIST as malignant, the mass must be >5 cm and must have >5 mitoses/50 hpf (2, 3).

The features of this GIST, notably the young age of the patient, female gender, multi-nodularity, hypercellular area with rhabdoid features, and lymph node metastasis, raise the suspicion for an SDH (succinate dehydrogenase)-deficient GIST (4).

References:

Abhirup B, Kaushal K, Sanket M, et al. Malignant hepatic perivascular epithelioid cell tumor (PEComa) – case report and a brief review. Journal of the Egyptian National Cancer Institute. 2015;27:239–242.

Fletcher CD1, Berman JJ, Corless C, Gorstein F, Lasota J, Longley BJ, Miettinen M, O'Leary TJ, Remotti H, Rubin BP, Shmookler B, Sobin LH, Weiss SW. Diagnosis of gastrointestinal stromal tumors: A consensus approach. Hum Pathol. 2002 May;33(5):459-65.

Paiva CE, Moraes Neto FA, Agaimy A, et al. Perivascular epithelioid cell tumor of the liver coexisting with a gastrointestinal stromal tumor. World J Gastroenterol. 2008;14, 5: 800-802.

Boikos SA, Pappo AS. Molecular Subtypes of KIT/PDGFRA Wild-Type Gastrointestinal Stromal Tumors: A Report From the National Institutes of Health Gastrointestinal Stromal Tumor Clinic. JAMA Oncol. doi:10.1001/jamaoncol.2016.0256.

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