Clinical history: A 34-year-old lady underwent EUS-FNA of a well-circumscribed pancreatic tail nodule. What are the findings from the following images?
- Highly cellular aspirate with papillary-like formations comprising delicate vascular cores covered by loosely adhered neoplastic epithelial cells ("spinning" off)
- Small clusters and scattered dispersed epithelial cells in the background
- Epithelial cells contain eccentric reniform nuclei with mild nuclear pleomorphism
- Nuclear grooves may be seen
- Small nucleoli may be present
- Finely distributed chromatin
- Some nuclei exhibit nuclear inclusions
- Abundant finely vacuolated cytoplasm with perinuclear vacuoles
The following differential diagnoses show a degree of cytomorphologic overlap and the key distinguishing features include
- Solid pseudopapillary neoplasm
- Low-power: Papillary-like structures with delicate to hyalinised vascular stalks (important diagnostic feature) and relative cellular discohesion
- High power: Reniform nuclei with nuclear grooves and perinuclear vacuoles
- Neuroendocrine tumour
- Low-power: Loosely cohesive groups, pseudorosettes and single plasmacytoid cells
- High-power: Round to plump oval nuclei, stippled chromatin and inconspicuous nucleoli
- Acinar cell carcinoma
- Low-power: Acinar architecture with scattered bare nuclei
- High-power: Fragile cytoplasm with spilled zymogen granules and single prominent nucleolus
The non-discriminating features which may be shared by these tumours include:
- Low-power pattern of small cell clusters and scattered single cells which appear relatively uniform
- Plasmacytoid neoplastic cells with eccentric, round to oval shaped nuclei
- Delicate cytoplasm with microvacuoles
There is diffuse nuclear expression of beta-catenin and LEF1 by the tumour cells. Synaptophysin is also focally positive; this is a potential pitfall where the tumour may be mistaken as a neuroendocrine tumour, although the latter is likely to show diffuse positivity. Identification of pseudopapillae with hyalinised vascular stalks and nuclear expression of beta-catenin is key to the diagnosis.
Solid pseudopapillary neoplasm
- Uncommon tumour (1 to 2% of pancreatic exocrine neoplasms) of low malignant potential
- Predominantly in adolescent girls and young women
- Slight preference for pancreatic tail
- Histogenesis unclear – possible genital ridge origin
- Somatic mutation in exon 3 of CTNNB1 gene
- A rare subset of cases may be associated with familial adenomatous polyposis
- Well-demarcated tumours with solid areas, pseudocystic spaces and haemorrhagic necrosis
- The presence of hyalinised vascular stalk with clinging neoplastic cells is a key morphologic feature
- Highly divergent immunohistochemical profile
- Positive: Beta-catenin (nuclear), cyclin D1, alpha-1 antitrypsin, CD56, CD10, PR receptor, synaptophysin (focal and a pitfall)
- Recent studies show high rate of diffuse nuclear expression of LEF1, AR and TFE3 (1)
- Kim, E. K., Jang, M., Park, M., & Kim, H. (2017). LEF1, TFE3, and AR are putative diagnostic markers of solid pseudopapillary neoplasms. Oncotarget, 8(55), 93404–93413. https://doi.org/10.18632/oncotarget.21854
Remaining information cited from: Klöppel, G., Klimstra, D. S., Basturk, O., Notohara, K. Solid pseudopapillary neoplasm. (2019). In: WHO Classification of Tumours: Digestive system tumours (5th edn). Lyon; IARC.
Case writer: Dr Noel Chia