APC-rearranged solid pseudopapillary neoplasm-pancreatic neuroendocrine tumor collision tumor: a molecularly resolved case report.

Solid-pseudopapillary neoplasm (SPN) is driven by CTNNB1 mutations, whereas pancreatic neuroendocrine tumors (PanNETs) harbor MEN1/DAXX/ATRX alterations. A true collision of the two entities has never been genetically proven. A 34-year-old man presented with a 4.2 cm pancreatic-tail mass and innumerable liver metastases. Distal pancreatectomy disclosed intimately admixed yet distinct SPN (90%) and G1 PanNET (10%). Targeted NGS revealed an in-frame APC rearrangement (Ex9-Int15); CTNNB1, MEN1, DAXX and ATRX were wild-type. Following distal pancreatectomy and radiofrequency ablation of liver metastases, the patient remains asymptomatic with no evidence of disease progression at 9-month follow-up. This is the first molecularly confirmed SPN-PanNET collision tumor driven by APC loss rather than CTNNB1 mutation. The case highlights the value of comprehensive genomic profiling when morphologic overlap obscures diagnosis and suggests that APC-driven SPNs may be more aggressive than previously thought.