Metastasis of a gastrointestinal stromal tumor (GIST)
GIST is a tumor entity that belongs to the group of soft tissue sarcomas. It primarily affects patients between the ages of 60 and 65; however, familial cases may present at an earlier age. GIST, which occurs most frequently in the stomach and small intestine, is thought to arise from mesenchymal cells, the interstitial cells of Cajal, part of the autonomic nervous system of the gastrointestinal tract (1). The tumor cells typically harbor a driver mutation in CD117 (tyrosine protein kinase KIT receptor) or in approximately 10% cases, mutations in the platelet derived growth factor receptor A (PDGFRA receptors) (2,3). Of note, cKIT and PDGFRA mutations are mutually exclusive. Although historically considered benign, metastatic potential varies according to location and size of the tumor (>5cm) and mitotic count (>5/50 hpf) (4). GIST commonly metastasizes to the liver (65%) and peritoneum (21%) (5).
There is a lower propensity for bone metastases, ranging from 3-6% in larger studies (6). GIST that develops outside the gastrointestinal tract is termed extra gastrointestinal stromal tumor (EGIST) (7). A rare variant is thought to originate from neuronal cells of the intestine the gastrointestinal autonomic nerve tumor (GANT) (8).
The differential diagnosis of dural-based neoplasms is extensive and can be diagnostically challenging. Primary considerations for tumors with similar morphologic features encompass atypical or even anaplastic meningioma (>20 mitoses/10 hpf), followed by a solitary fibrous tumor (SFT), malignant peripheral nerve sheath tumor (MPNST) and other sarcomas. In fact, evidence of CD34 positivity may mislead towards the diagnosis of SFT/ hemangiopericytoma. In contrast, the lack of STAT6 immunolabeling militates against SFT/hemangiopericytoma and favors meningioma or MPNST. However, the history of multiple lesions in the intestines and liver should alert the pathologist to consider the possibility of a GIST metastasis. In fact, the combined strong expression of CD117 and the marker "discovered on GIST 1" (Dog1) confirms the diagnosis. The other biopsies from the patient showed similar histomorphological and immunohistochemical profiles.
Even though the likelihood for GIST metastases is very rare, the present case illustrates that in unresolved cases of dural-based tumor masses, the differential diagnosis of tumors mimicking meningioma should also include GIST.
Contributed by Henning Leske, Elisabeth Rushing, Rene Bernays