Pancreatic/Peripancreatic Spindle Cell Lesions Cytology: A 15-Year Review

Introduction/Objective Spindle cell lesions (SCL) are diagnostically challenging, especially on cytology specimens where entities have overlapping features. Neoplastic and non-neoplastic SCL are uncommonly encountered in the pancreas/peripancreatic tissue. The sensitivity and specificity of EUS-FNA of pancreatic lesions both approach 95%. In this study, we assess the frequency of SCL found in pancreas/peripancreatic tissue on cytology specimens, the frequency of performing IHC stains and the most useful IHC panels. We also evaluate histology-cytology discrepancies and pitfalls. Methods A retrospective analysis of all pancreas/peripancreatic cytology specimen results between January 2004 - August 2019 was conducted. A total of 5,132 cases were identified. The number of spindle cell lesions was 27 (0.52%), with surgical pathology results available for 15 cases (55%). IHC stains were performed on 18 cell blocks (66%) and 9 surgical pathology specimens (60%). Results Of the 27 SCL identified, 22 lesions were neoplastic (81%), and 5 lesions were non-neoplastic (19%). The Neoplastic cases were: 10 GISTs (37%), 4 spindle cell lesions, NOS (14.8%), 2 metastatic sarcomas (7.4%), 1 pheochromocytoma (3.7%), 1 leiomyoma (3.7%), 1 schwannoma (3.7%), 1 malignant fibrous histiocytoma (3.7%), 1 granular cell tumor (3.7%), and 1 neuroendocrine carcinoma (3.7%). Of the neoplastic cases, 10 were lesions originating in a different organ with direct extension/distant metastasis to the pancreas (71%), with the most common organ being the stomach, 6 cases (60%). The non-neoplastic cases were: 4 granulomas (14.8%), and 1 accessory spleen (3.7%). IHC stains were performed on 18 cell blocks (66%), and attempted unsuccessfully on 2 cell blocks. The most commonly utilized stains were: CD117, 15 cases (83%), SMA, 11 cases (61%), S-100, 9 cases (50%), CD34, 5 cases (27%) and Cytokeratin, 5 cases (27%). IHC stains assisted with proper classification in 9 cytology cases (50%). There was one interpretation error*, and the histology-cytology discrepancy rate was 6%. Conclusion Pancreatic and peripancreatic spindle cell lesions are uncommon (520/100,000), and are particularly challenging on cytology specimens. If neoplastic, the majority originate in an organ other than the pancreas. If non- neoplastic, the majority are granulomas. Immunohistochemical staining is required for proper classification. And in this small series, cytology is highly accurate for diagnosis (96%).