Perigastric solitary fibrous tumor (SFT) diagnosed on fine needle aspiration: A case report and review of literature

Abstract

Solitary fibrous tumor (SFT) is a mesenchymal tumor initially described in the pleura. When the tumor is located in the pleura and the classic histologic findings are present, the diagnosis of SFT can be straightforward. However, the cytologic diagnosis of perigastric SFT can be challenging due its rarity with only one cytology case report. Another confounding factor is its potential mimicry with other perigastric/gastric mesenchymal tumors. Herein, we report a case of perigastric SFT diagnosed on cytology in conjunction with immunohistochemical stains. The patient is a 79-year-old woman who presented with an enlarging perigastric mass on computerized tomography scan which was highly concerning for a saccular aneurysm. Endoscopic ultrasound (EUS) revealed a 6.6 cm hypoechoic lesion abutting the stomach. An EUSguided fine needle aspiration was performed. The smears showed singly scattered to clusters of bland spindle cells with scant cytoplasm dispersed in a bloody background. The cell block showed similar spindle cells focally supported by a collagenized stroma. Immunohistochemical stains performed on the cell block showed the tumor cells were positive for CD34, BCL2, and STAT6 and negative for CD117, DOG1, CD31, ERG-ENDO, AE1/AE3, S-100, desmin, and synaptophysin, supporting the diagnosis of solitary fibrous tumor.

Cytomorphological spectrum of solitary fibrous tumour: revisited

“…Further, smears may frequently show a combination of several findings. Also, the cell block sections can simulate the “patternless” haphazard arrangement seen on histopathology 3 . Therefore, it is difficult to subtype the SFTs as benign or malignant based on only the FNA findings.…”

“…Of these, CD34 is considered to be the most helpful diagnostic stain. A highly sensitive and specific surrogate marker is STAT6, which gives strong and exclusive nuclear positivity in SFTs, while in other entities, the staining is cytoplasmic or low nuclear 3,14,36,37 1,13,15,27,28,37–40 …”

“…A highly sensitive and specific surrogate marker is STAT6, which gives strong and exclusive nuclear positivity in SFTs, while in other entities, the staining is cytoplasmic or low nuclear. 3,14,36,37 However, this immunoexpression may not be evident in dedifferentiated forms. 1,13,15,27,28,[37][38][39][40] On cytomorphology, SFT is a diagnostic ordeal as the morphological variability is further enhanced on cytology smears.…”

“…Solitary fibrous tumours (SFTs) are soft tissue tumours of fibroblastic origin 1 . These tumours were first reported in pleura but are also detected at extra‐pleural locations 2,3 . The underlying genetic pathology is a paracentric inversion in chromosome 12q, leading to NAB2‐STAT6 gene fusion, which further activates several growth factor pathways 1,2,4 .…”

“…1 These tumours were first reported in pleura but are also detected at extra-pleural locations. 2,3 The underlying genetic pathology is a paracentric inversion in chromosome 12q, leading to NAB2-STAT6 gene fusion, which further activates several growth factor pathways. 1,2,4 Morphologically, these tumours are composed of spindle-shaped cells along with prominent, dilated and branching blood vessels, described as "staghorn vasculature".…”