Subtitle: Worst pattern of invasion (WPOI 1–5) in oral squamous cell carcinoma: definitions, the 1 mm satellite rule, the Brandwein-Gensler risk model, depth of invasion vs tumour thickness, AJCC 8 pT staging and 10 MCQs.
Author: PathologyMCQ Editorial Board
Category: Head and Neck Pathology
Last Updated: October 2026
Read Time: 7 minutes
At-a-Glance
- WPOI grades the most aggressive invasion pattern at the tumour front, from 1 (pushing) to 5 (dispersed satellites).
- WPOI-5 = tumour satellites ≥1 mm from the main tumour or nearest satellite; it predicts local recurrence.
- The Brandwein-Gensler risk model adds perineural invasion and lymphocytic host response.
- Depth of invasion (DOI) is measured from the adjacent normal basement membrane and drives AJCC 8 pT.
- Tumour thickness is measured from the surface and is not the same as DOI.
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WPOI Types 1–5
| WPOI | Pattern | Risk |
|---|---|---|
| 1 | Broad pushing border | Low |
| 2 | Finger-like (broad pseudopods) pushing projections | Low |
| 3 | Large separate islands, more than 15 cells per island | Low |
| 4 | Small islands (≤15 cells), cords or single cells | Intermediate |
| 5 | Tumour satellites ≥1 mm from main tumour or next satellite, in non-fibrotic stroma | High |
Assess WPOI at the worst area of the advancing front. Satellites must be separated by at least 1 mm of non-fibrotic tissue; islands closer than 1 mm count as WPOI-4. Perineural or lymphovascular tumour 1 mm or more away also counts as WPOI-5.
Brandwein-Gensler Risk Model
| Feature | Points |
|---|---|
| WPOI-5 | 3 |
| WPOI-4 | 1 |
| Perineural invasion of large nerves (≥1 mm diameter) | 3 |
| Perineural invasion of small nerves | 1 |
| Limited lymphocytic host response | 3 |
| Intermediate lymphocytic host response | 1 |
| Total 0 = low risk; 1–2 = intermediate; ≥3 = high risk |
Because WPOI-5 alone scores 3, it places even a small tumour in the high-risk group, which is why CAP asks pathologists to report it.
Depth of Invasion vs Tumour Thickness
| Measure | From | To | Use |
|---|---|---|---|
| Depth of invasion (DOI) | Horizon at the basement membrane of the closest adjacent normal mucosa | Deepest point of invasion (plumb line) | AJCC 8 T stage |
| Tumour thickness | Tumour surface (or ulcer base) | Deepest point of invasion | Descriptive; not for staging |
AJCC 8 pT Staging (Oral Cavity)
| pT | Criteria |
|---|---|
| pT1 | ≤2 cm and DOI ≤5 mm |
| pT2 | ≤2 cm with DOI >5 mm and ≤10 mm, or >2 cm and ≤4 cm with DOI ≤10 mm |
| pT3 | >4 cm, or any tumour with DOI >10 mm |
| pT4a | Invades adjacent structures (cortical bone of mandible or maxilla, maxillary sinus, skin of face) |
| pT4b | Invades masticator space, pterygoid plates or skull base, or encases internal carotid artery |
Test Yourself: 10 MCQs
WPOI and oral SCC: 10 MCQs
Patterns of invasion, DOI and AJCC staging, with instant explanations.
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Exam Pearls
- WPOI-5 = satellites ≥1 mm away; closer islands are WPOI-4.
- WPOI-5 alone = high risk in the Brandwein-Gensler model.
- DOI from the adjacent basement membrane, not from the tumour surface.
- DOI >10 mm = at least pT3 (AJCC 8).
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References
- Brandwein-Gensler M, et al. Oral squamous cell carcinoma: histologic risk assessment, but not margin status, is strongly predictive of local disease-free and overall survival. Am J Surg Pathol. 2005;29:167–78.
- College of American Pathologists. Protocol for the Examination of Specimens From Patients With Cancers of the Lip and Oral Cavity. Current version.
- Amin MB, et al., eds. AJCC Cancer Staging Manual. 8th ed. Springer; 2017.
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