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Somatostatin receptor imaging in neuroendocrine tumours
Well-differentiated neuroendocrine tumours strongly express somatostatin receptor type 2, so PET with Ga-68 DOTATATE (or DOTATOC/DOTANOC, or Cu-64 DOTATATE) is their central staging study — and in less differentiated tumours expression falls and FDG rises ("flip-flop").
Why it matters in the exam
The exam asks which study to choose by tumour grade: G1 and G2 (low Ki-67) — SSTR PET; G3 and poorly differentiated neuroendocrine carcinoma — FDG, and sometimes both to identify aggressive lesions (FDG-positive and SSTR-negative) that will not respond to receptor-targeted treatment. SSTR PET replaced In-111 pentetreotide (Octreoscan) because it is more sensitive, faster and gives a lower radiation dose.
Normal distribution: the spleen takes up most, then the kidneys, adrenals, pituitary, liver and thyroid. A classic pitfall is uptake in the uncinate process of the pancreas, which looks like a tumour. An accessory spleen (splenule) takes up strongly. Other positives: meningioma (also for suspected recurrence after surgery), inflammation and active osteoblasts. Long-acting somatostatin analogues compete for the receptor — the study is done just before the next dose (guidelines generally allow up to about 3–4 weeks after the injection), and a short-acting preparation is stopped a day before. This avoids competition for the receptor, so tumour uptake reflects its true expression and not the last drug dose.
The study is used for staging, finding an occult primary, follow-up, and selecting patients for Lu-177 DOTATATE therapy: lesion uptake equal to or higher than the liver (Krenning scale 3–4 or a PET equivalent) is a condition for treatment. A benign insulinoma sometimes expresses little SSTR2, and there exendin PET targeting the GLP-1 receptor is more sensitive. F-18 DOPA is useful in small-bowel tumours and phaeochromocytoma.
Key points
- Well-differentiated NET — Ga-68 DOTATATE PET.
- Poorly differentiated NET — FDG PET; flip-flop.
- The spleen is the organ with the most uptake.
- Pitfalls: uncinate process and accessory spleen.
- Lu-177 DOTATATE needs uptake equal to or above the liver.
Summary table
| Situation | Preferred study | Note |
|---|---|---|
| Well-differentiated NET G1–G2 | Ga-68 DOTATATE PET | Staging, occult primary, follow-up |
| NET G3 or NEC | FDG PET | Flip-flop |
| Before Lu-177 DOTATATE | SSTR PET | Uptake equal to or above the liver |
| Benign insulinoma | Exendin PET (GLP-1) | SSTR2 sometimes low |
| Meningioma — suspected recurrence | Ga-68 DOTATATE PET | Separating from scar |
A free exam question
לאיזה סוג ממאירות של הלבלב יש לבדיקת FDG PET/CT את הרגישות הגבוהה ביותר? (the question as examined, in Hebrew)
- א. IPMN ((Intra-ductal Papillary Mucinous Neoplasm של הלבלב
- ב. גידול נוירואנדוקריני )NET ( עם מדד פרוליפרציה נמוך )5%<Ki-67
- ג. Invasive Mucinous Adenocarcinoma
- ד. אדנוקרצינומה בהתמיינות נמוכה )Differentiated Poorly
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Sources
- Joint EANM/SNMMI Procedure Guideline for SSTR PET Imaging of Neuroendocrine Tumours, 2023 — Preparation, physiological distribution and pitfalls
- ENETS Guidance Paper: Imaging in Neuroendocrine Neoplasms, 2023 — Choice of SSTR PET versus FDG PET
- NCCN Guidelines: Neuroendocrine and Adrenal Tumours, 2025 — Imaging recommendations
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.