Diagnostic Utility of LEF1 Immunostain in Cytology Specimens of Solid Pseudopapillary Neoplasm of Pancreas

Solid pseudopapillary neoplasm (SPN) of the pancreas is a rare neoplasm. Diagnosis of SPN requires an integrated approach with aid of radiology, biopsy, cytology, and immunohistochemical stains. Although morphological features in combination with nuclear positivity of β-catenin IHC have been the gold standard of SPN diagnosis, but overlapping morphology and immunohistochemical findings with other entities in differential diagnoses such as pancreatic neuroendocrine tumors and pancreatic ductal adenocarcinoma make the diagnosis of SPN difficult particularly in limited cytology specimens. Lymphoid enhancer-binding factor 1 (LEF1), a key player in the Wnt signaling pathway, has shown promising diagnostic utility in SPN in recent literatures. Methods: In this retrospective study, we evaluated the diagnostic utility of LEF1 IHC in SPN in cytology specimens. LEF1 IHC was performed and compared with β-catenin, synaptophysin, and chromogranin immunostains in 13 SPN and 23 pancreatic neuroendocrine tumors (PanNETs) cytology cases with retrievable cell blocks. Results: LEF1 was positive in 13 of 13 (100%) SPNs and was negative in all PanNETs (0%). Conclusion: LEF1 shows 100% sensitivity and specificity in cytology specimens for SPN and can be valuable immuno­stain in the diagnosis of SPN in cytology cell blocks.