Abstract

Introduction: Somatostatin receptor PET/CT with 68-gallium–labeled tracers (e.g., 68Ga-DOTATATE) is the gold standard imaging modality for well-differentiated neuroendocrine tumors (NETs), whereas 68Ga-PSMA PET/CT is routinely used in prostate cancer. PSMA PET can incidentally localize to other malignancies due to PSMA expression in the tumor neovasculature, but its role in NETs is still unclear.
Case: We present the case of a 40-year-old male with metastatic ileal NET (midgut carcinoid) who had undergone 68Ga-DOTATATE and 68Ga-PSMA PET/CT imaging. DOTATATE PET/CT showed intense radiotracer uptake in the primary ileal tumor and multiple liver metastases (SUVmax ~15), confirming strong somatostatin receptor expression. In striking contrast, PSMA PET/CT demonstrated no abnormal uptake in any of the lesions. The patient had no history of prostate cancer.
Discussion: This case illustrates the rare discordance between DOTATATE and PSMA tracer uptake in NET. Prior literature reports PSMA-avid disease in some NETs (especially pancreatic NETs), which is attributed to PSMA expression in tumor-associated neovasculature. Our midgut NET case showed an absence of PSMA uptake, suggesting heterogeneity in PSMA expression across NET subtypes and tumor microenvironments.
Conclusion: 68Ga-PSMA PET can be negative in DOTATATE-positive midgut NETs, underscoring the importance of somatostatin receptor imaging for disease evaluation and caution against assumptions of universal PSMA avidity in NETs.

Key words: Ileal neuroendocrine tumor, 68Ga-DOTATATE, 68Ga-PSMA, PET/CT, somatostatin receptor imaging, discordance, theranostics, midgut carcinoid,neoangiogenesis.