One Tumor, Two Readings: Interpreting DOTATATE Uptake in Biopsy-Proven Pancreatic Adenocarcinoma

Background

Pancreatic ductal adenocarcinoma (PDAC) accounts for the vast majority of pancreatic malignancies and carries a five-year survival rate of approximately twelve percent. Pancreatic neuroendocrine neoplasms are rare mimics with markedly different prognoses and treatment strategies. A diagnostic challenge arises when biopsy-proven adenocarcinoma coexists with imaging features suggesting neuroendocrine biology, raising the possibility of a Mixed Neuroendocrine-Non-neuroendocrine Neoplasm (MiNEN). Dual-tracer PET phenotyping, which combines FDG-PET with somatostatin receptor (SSTR)-targeted imaging, complements histopathology by mapping whole-body tumor biology and identifying therapeutic targets that a single-site biopsy cannot capture. NCCN Guidelines endorse this combined imaging approach for neuroendocrine tumors while recommending treatment directed at the most aggressive histologic component in mixed histologies. This case matters because it demonstrates how functional imaging can reveal actionable biology beyond tissue diagnosis, refining prognosis and expanding future therapeutic options without altering appropriate first-line therapy.

Case Presentation

An elderly female presented with abdominal distension and left flank pain of several days' duration. CT imaging revealed a pancreatic mass measuring 5.4 by 4.2 centimeters with vascular encasement and splenic vein thrombosis. CA 19-9 was elevated at 209 U/mL in the absence of jaundice, validating it as a true tumor marker rather than a biliary artifact. Endoscopic ultrasound-guided fine needle aspiration cytology confirmed pancreatic ductal adenocarcinoma arising in a background of intraductal papillary mucinous neoplasm with high-grade dysplasia. FDG-PET/CT demonstrated an FDG-avid pancreatic mass without distant metastases. A subsequent 64Cu-DOTATATE PET/CT revealed unexpected SSTR uptake with a maximum SUV of 7.5 in the pancreatic head and 8.0 in the body and tail.

Findings

The combined imaging established a dual-positive SSTR+/FDG+ phenotype, classified as D2 on the NETPET scale. The NETPET classification stratifies tumors into D1 (SSTR+/FDG-, most favorable), D2 (SSTR+/FDG+, intermediate), and D3 (SSTR-/FDG+, least favorable) prognostic categories, and FDG positivity independently predicts reduced survival after controlling for tumor grade. Because the biopsy confirmed adenocarcinoma and the elevated CA 19-9 supported a dominant PDAC component, systemic therapy with gemcitabine and nab-paclitaxel was initiated in accordance with NCCN guidance. The SSTR-avidity simultaneously established eligibility for future peptide receptor radionuclide therapy should PDAC-directed therapy fail.

Discussion & Conclusion

This case illustrates the complementary roles of histopathology and dual-tracer PET phenotyping in diagnostically challenging pancreatic neoplasms. Tissue diagnosis remains the gold standard for treatment selection, yet functional imaging revealed an SSTR-positive component not captured by single-site biopsy, raising the possibility of MiNEN and providing prognostic information invisible on cytology alone. The D2 phenotype refined risk stratification while preserving guideline-concordant chemotherapy. Dual-tracer PET phenotyping should be considered when clinical, biochemical, or imaging features are discordant with initial pathology, as it can uncover actionable biology and expand therapeutic options.