Solid Pseudopapillary Neoplasm of the Pancreas: Diagnostic Concordance and Clinicopathologic Correlation of Fine-Needle Aspiration and Long-Term Outcomes.

INTRODUCTION: Solid pseudopapillary neoplasm (SPN) is a rare pancreatic tumor with low malignant potential and unclear cell of origin and pathogenesis. Fine-needle aspiration (FNA) is frequently used for preoperative diagnosis, yet correlation with resection specimens and long-term follow-up remains limited in the literature. MATERIALS AND METHODS: We retrospectively identified all patients diagnosed with SPN by pancreatic FNA at a single institution (2016-2025). Cytology preparations included smears with or without rapid on-site evaluation and ancillary immunohistochemistry performed on cell blocks when available. Surgical pathology, when performed, was reviewed for diagnostic concordance and adverse features. Clinical outcomes were assessed by chart review. RESULTS: Seven patients were identified (female-to-male ratio = 6:1; median age = 29 years, range = 18-53 years). Tumors most commonly involved the tail (5/7) and measured a median of 6.0 cm (range = 2.6-14.0). Pancreatic FNA rendered a definitive diagnosis of SPN in six cases (6/7). Six patients underwent resection, and surgical pathology confirmed SPN in all resected tumors (6/6). Lymphovascular invasion was absent in all resected cases; perineural invasion was present in one case. At last follow-up (median = 41 months, range = 4-119), all patients were alive. One patient developed liver metastasis eight years after the initial diagnosis. CONCLUSIONS: Pancreatic FNA demonstrated excellent diagnostic concordance and clinicopathologic correlation for SPN with available resections. Despite overall indolent behavior, late metastatic disease can occur, supporting the need for long-term surveillance.