Lavisha S Punjabi¹, Clement Chun-Ho Wu^2,3,4, Samuel Lim Jun Ming²,  Albert Low Su Chong⁵, Tony Lim Kiat Hon^1,4. 

¹ Department of Anatomical Pathology, Singapore General Hospital; ² Department of Gastroenterology, Singapore General Hospital; ³ Division of Gastroenterology, Johns Hopkins Hospital; ⁴ Duke-NUS Medical School; ⁵ Department of Diagnostic Radiology, Singapore General Hospital. 

Mesenchymal tumours involving the pancreas are uncommon, and their subtyping on cytology is challenging. 

A 65-year-old male presented for loss of weight. CT showed an ill-defined mild low density change at the pancreatic head. MRCP showed a 3.4cm solid lesion, T2-w hypointense relative to the pancreas, prompting consideration of leiomyoma or fibromatosis as differentials.

The patient then underwent EUS-FNA. A 3.4cm homogenous iso-echoic mass was visualised and sampled. Smears and cell block showed short spindle cells embedded in fragments of collagenous stroma. The spindle cells showed uniform, ovoid nuclei with granular chromatin. There was no high grade atypia nor necrosis. The spindle cells were positive for STAT6, CD34, and BCL2. The cytological findings are indicative of solitary fibrous tumour (SFT). 

Confirmation with molecular studies is ideal, but was hampered by limited material, prompting careful clinico-radiological correlation. The pancreas is an unusual location for SFT¹, and only rare cases of cytological diagnosis at this site have been reported^2,3. Rarely, other tumours, such as dedifferentiated liposarcoma may co-amplify STAT6, and demonstrate SFT-like morphology; however the small size and the absence of a fat component on radiology rendered this improbable. Hence, the consensus at multi-disciplinary team discussion was for follow-up surveillance imaging. 

References: 

1.     Yavas A, Tan J, Ozkan HS, Yilmaz F, Reid MD, Bagci P, Shi J, Shia J, Adsay V, Klimstra DS, Basturk O. Solitary fibrous tumor of the pancreas: analysis of 9 cases with literature review. The American Journal of Surgical Pathology. 2023 Nov 1;47(11):1230-42.

2.     Rogers C, Samore W, Pitman MB, Chebib I. Solitary fibrous tumor involving the pancreas: report of the cytologic features and first report of a primary pancreatic solitary fibrous tumor diagnosed by fine-needle aspiration biopsy. Journal of the American Society of Cytopathology. 2020 Jul 1;9(4):272-7.

3.     Jones VM, Wangsiricharoen S, Cornea V, Bocklage TJ, Ali SZ, Allison DB. Cytopathological characteristics of solitary fibrous tumour involving the pancreas by fine needle aspiration: Making an accurate preoperative diagnosis in an uncommon location. Cytopathology. 2022 Mar;33(2):222-9.