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PET/CT in gastrointestinal cancers
In gastrointestinal tumours FDG PET/CT is not the first diagnostic study but a study for staging and finding occult disease — mainly in oesophageal cancer before radical treatment and in suspected recurrence of colorectal cancer with a rising CEA and an equivocal CT.
Why it matters in the exam
In oesophageal cancer the usual staging set is chest and abdominal CT, endoscopic ultrasound (EUS) to assess depth of invasion and nearby nodes, and PET/CT to find distant metastases not seen on CT, when there is no evidence of metastatic disease. PET also assesses response to neoadjuvant treatment. In gastric cancer PET is less useful, because mucinous and signet ring types take up FDG weakly, and in a superficial T1 tumour there is no indication; it is considered in locally advanced tumours when CT shows no metastases.
In colorectal cancer PET/CT is not routine staging, but it is indicated when CEA rises and CT is negative, before resection of liver or lung metastases (to avoid operating on a patient with widespread disease), and in separating a scar after surgery or radiation in the pelvis from recurrence. Unexpected focal colonic uptake on PET done for another reason calls for colonoscopy, because a considerable share of foci are adenomas or cancer. Metformin causes diffuse, not focal, bowel uptake.
In liver tumours, well-differentiated HCC takes up FDG weakly, and high uptake suggests a poorly differentiated tumour and a poor prognosis; colorectal liver metastases take up well. In pancreatic tumours PET helps in staging and in separating chronic inflammation from tumour only in some cases. In well-differentiated neuroendocrine tumour Ga-68 DOTATATE is preferred. In GIST, PET shows an early response to imatinib, within days, long before a change in size.
Key points
- Oesophageal cancer — PET/CT for distant metastases before radical treatment.
- Gastric cancer — PET limited, not in T1 tumours.
- Rising CEA with negative CT — PET/CT.
- Before liver metastasectomy — PET/CT.
- GIST — early response to imatinib on PET.
Summary table
| Tumour | Role of PET/CT | Note |
|---|---|---|
| Oesophageal cancer | Staging for distant metastases, response to neoadjuvant treatment | With CT and EUS |
| Gastric cancer | Limited, in advanced tumours | Mucinous and signet ring take up weakly |
| Colorectal cancer — recurrence | Rising CEA with negative CT, before metastasectomy | Focal colonic uptake — colonoscopy |
| HCC | Prognostic | Well differentiated — negative |
| GIST | Early response to imatinib | Uptake falls within days |
A free exam question
מה היתרון העיקרי של PET/CT עם FDG בגישה טיפולית של מטופל עם סרטן הוושט בהשוואה לסונוגרפיה אנדוסקופית )EUS ?( (the question as examined, in Hebrew)
- א. רגישות גבוהה יותר לזיהוי נגעים מוקוסליים
- ב. הערכה מדויקת יותר של עומק החדירה המקומית T-staging
- ג. זיהוי טוב יותר של גרורות מרוחקות
- ד. מדידה מדויקת יותר של גודל הגידול הראשוני
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Sources
- NCCN Guidelines: Esophageal and Esophagogastric Junction Cancers; Gastric Cancer, 2025 — Workup and staging
- ESMO Clinical Practice Guidelines: Metastatic Colorectal Cancer, 2023 — Imaging for recurrence and resectability
- EANM Procedure Guidelines for Tumour Imaging: FDG PET/CT Version 2.0, 2015 — Indications in gastrointestinal tumours
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.