Solitary fibrous tumor of the stomach with high-grade sarcomatous dedifferentiation

Abstract

Solitary fibrous tumors (SFT) are uncommon fibroblastic mesenchymal neoplasms that display a wide range of histologic behaviors. These tumors, which are estimated to account for 2% of all soft tissue neoplasms, typically follow a benign clinical course. However, it is estimated that 10-30% of SFTs are malignant and demonstrate aggressive behavior with local recurrence and metastasis up to several years after surgical resection. We report a case of SFT arising from the stomach, which is an exceptionally rare finding and has been reported only six times in the literature. Our case was complicated by diagnostic dilemma with GIST, highlighting the challenges of diagnosing and characterizing SFTs. Additionally, this tumor was associated with dedifferentiation into undifferentiated pleomorphic sarcoma. To our knowledge, there are no documented cases of a malignant SFT arising from the stomach to demonstrate dedifferentiation into an undifferentiated pleomorphic sarcoma.

Figure 1:

(A) CT abdomen demonstrates large heterogenous mass. (B) MRI coronal images display a heterogeneous mass on T1 (left) and T2 signal (right) arising from the submucosa with components restricting diffusion.

Figure 2:

(A) On fine needle aspiration cytology, bland spindle cells are present. (B) On cell block, the lesional cells stains strongly with CD34 immunostain. (C) On repeat fine needle aspiration cytology, STAT6 displays strong nuclear staining. (D) Gross image of the resection specimen revealing a tan solid and cystic lobulated submucosal mass.

Figure 3:

(A) Liver metastastectomy demonstrating ‘fish fleshy’ consistency of metastatic sarcoma. (B) Metastasic lesion demonstrating dense solid sheets of spindled to round high-grade pleomorphic nuclei with large, prominent nucleoli, numerous mitotic figures (including atypical, bizarre forms) and large areas of geographic necrosis.