# FAPI PET as the workup for MCED positives

Source: https://onco.cc/ideas/idea-mced-plus-fapi/  
OnCo record `idea-mced-plus-fapi` (Idea). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

When a blood test says 'cancer signal, origin unclear', a FAPI PET scan may find it where FDG cannot.

## Summary

When a blood test reports a cancer signal of unclear origin, this idea sends the patient for FAPI PET/CT rather than FDG PET as the first-line work-up. Many MCED-positive patients have no cancer found on standard imaging, which creates anxiety and cost, whereas FAPI PET is more sensitive than FDG in pancreatic, gastric, low-grade and peritoneal disease, exactly the cancers MCED promises to catch, and has low background in liver, brain and bowel. The test is a prospective diagnostic study nested in a Galleri deployment such as the NHS or a PATHFINDER-like cohort, randomising FDG versus FAPI PET. Speculative in maturity, it addresses the bottleneck The hardest cancers are found late and is linked from the ideas on a 28-day MCED-positive resolution pathway and whole-population interception.

## Fields

- Kind: Idea
- Last checked: 2026-09-04
- Hypothesis: FAPI PET/CT increases the cancer detection rate and reduces time to diagnosis in MCED-positive, FDG-negative or tissue-of-origin-uncertain patients.
- Rationale: Complementary biology (stroma vs glucose); FAPI has low background in liver, brain, and bowel.
- Proposed test: Prospective diagnostic study nested in a Galleri deployment (e.g., NHS or PATHFINDER-like) randomising FDG vs FAPI PET as first-line workup.
- Maturity: speculative

## Sources

- PATHFINDER: the first prospective test of a multi-cancer blood test in people without symptoms (The Lancet 2023): https://doi.org/10.1016/S0140-6736(23)01700-2

## Connected records

- cancers: [Gastric & gastro-oesophageal junction cancer](https://onco.cc/cancers/gastric/), [Ovarian cancer](https://onco.cc/cancers/ovarian/), [Pancreatic ductal adenocarcinoma](https://onco.cc/cancers/pancreatic/)
- technologies: [FAPI PET](https://onco.cc/technologies/fapi-pet/), [FDG PET](https://onco.cc/technologies/fdg-pet/), [Multi-cancer early detection (MCED)](https://onco.cc/technologies/mced/)
- targets: [FAP](https://onco.cc/targets/fap/)
- drugs: [Galleri](https://onco.cc/drugs/galleri/)
- bottlenecks: [The hardest cancers are found late](https://onco.cc/bottlenecks/b-early-detection/)
- ideas: [A 28-day national pathway for people with a positive multi-cancer blood test](https://onco.cc/ideas/idea-prev-mced-positive-resolution-pathway/), [A whole-population cancer interception programme: risk-stratify every adult, detect and intercept early](https://onco.cc/ideas/idea-moon-population-interception/)

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