In esophageal cancer, can PET (positron emission tomography) be used for T staging, and if a pre‑operative biopsy shows invasion of the muscularis propria, should the TNM stage be based on the pathological result rather than the imaging assessment?

PET Cannot Be Used for T Staging in Esophageal Cancer

PET is not appropriate for T staging in esophageal cancer due to poor accuracy, and if a pre-operative biopsy demonstrates muscularis propria invasion, this represents pathological (not radiological) staging that supersedes imaging assessments.

PET Performance for T Staging

PET has limited and inadequate performance for determining T stage in esophageal cancer 1:

• Endoscopic ultrasound (EUS) is superior to PET for T staging - studies show EUS correctly stages 71-86.7% of primary tumors compared to only 33.3-42% for PET 2
• PET cannot differentiate high-grade dysplasia (Tis) from invasive cancer (T1), with only 45% sensitivity for Tis and 55% for T1 3
• For superficial/early cancers (T1), PET has particularly poor performance - missing 4 of 11 T1 lesions in one study, and showing only 46.7% accuracy for T1 staging 3, 4
• The poor spatial resolution of PET limits its ability to assess depth of tumor invasion through esophageal wall layers 1

Clinical Implication

The 2022 ESMO guidelines explicitly state that EUS should be used for T staging, not PET 5. PET's primary role is detecting distant metastases (M staging), where it demonstrates 67-97% specificity 1.

Understanding the Staging Nomenclature Issue

When a pre-operative biopsy shows muscularis propria invasion, this creates an important distinction:

This is Pathological Staging (pT)

• Any tissue obtained and examined by a pathologist generates a pathological stage (pT), not a clinical/radiological stage (cT)
• If the biopsy definitively shows invasion into muscularis propria, this is at minimum pT2 disease by definition
• This pathological information takes precedence over imaging for treatment planning

Key Distinction

• Clinical staging (cT) = based on imaging (CT, PET, EUS) and endoscopy without tissue proof of depth
• Pathological staging (pT) = based on microscopic examination of tissue specimens
• A biopsy showing muscularis propria invasion is pathological evidence, not radiological

Practical Algorithm

If pre-operative biopsy shows muscularis propria invasion:

1. Stage as pT2 (pathological, not clinical)
2. Complete staging with EUS for full T assessment and N staging
3. Use PET-CT for M staging (distant metastases) 5
4. Proceed with neoadjuvant therapy followed by surgery per guidelines 6

Common Pitfall: Do not downgrade pathologically-proven T2 disease based on imaging that suggests lower stage - the pathology supersedes the imaging when tissue diagnosis is available.

The final TNM designation would be reported as pT2 cN_ cM_ (pathological T, clinical N and M) until surgical resection provides complete pathological staging 5.