Classification of squamous cell carcinoma according to UICC TNM.
| T1 | Tumor ≤ 2 cm in greatest horizontal extent. |
| T2 | Tumor > 2 cm in greatest horizontal extent |
| T3 | Infiltration of deep extradermal structures (skeletal muscle, cartilage, bone, jaws, and orbits) |
| T4 | Infiltration of the base of the skull or the axial skeleton |
| Nx | Regional lymph nodes not assessable |
| N0 | No regional lymph node metastases |
| N1 | Solitary lymph node metastasis, maximum diameter |
| N2 | Solitary lymph node metastasis, maximum diameter ≥ 3 to 6 cm max. |
| Multiple lymph node metastasis, all with a max diameter ≤ 6 cm | |
| N3 | Lymph node metastasis with a diameter > 6 cm |
| M0 | No distant metastases present |
| M1 | Distant metastases present |
Classification of squamous cell carcinoma according to AJCC 2010.
| Tx | Primary tumor not assessable |
| T0 | No evidence of a primary tumor |
| Tis | Carcinoma in situ |
| T1 | Tumor ≤ 2 cm in greatest horizontal extent and a |
| T2 | Tumor > 2 cm in greatest horizontal extent and at least one high-risk feature a |
| Or tumor of any horizontal diameter with at least 2 high-risk features a | |
| T3 | Bony infiltration of maxilla, mandible, orbita, or os temporale/tibia |
| T4 | Infiltration of the skeletal bones or perineural infiltration of the base of the skull |
| Nx | Regional lymph nodes not assessable |
| N0 | No regional lymph node metastases |
| N1 | Solitary, ipsilateral lymph node metastasis, maximum diameter ≤ 3 cm |
| N2a | Solitary, ipsilateral lymph node metastasis, maximum diameter > 3 to ≤ 6 cm |
| N2b | Multiple, ipsilateral lymph node metastases, all with a maximum diameter ≤ 6 cm |
| N2c | Multiple, ipsilateral or contralateral lymph node metastases, all with a maximum diameter ≤ 6 cm |
| N3 | Lymph node metastasis with a diameter > 6 cm |
| Mx | Metastasis not assessable |
| M0 | No distant metastases present |
| M1 | Distant metastases present |
Legend
- AJCC: “American Joint Committee on Cancer.”
- M: metastasis, N “node”, T tumor.
- AHigh-risk characteristics: vertical tumor thickness ≥2 mm, Clark level ≥ 4, perineural invasion, tumor poorly or de-differentiated, localization auricle or hairy lip.
Classification by vertical tumor thickness with metastasis rate data.
| Tumor characteristics | Metastasis rates | |
| No risk (T1) | Vertical tumor thickness ≤ 2 mm | 0 % |
| Low risk (T2) | Vertical tumor thickness 2.01-6 mm | 4 % |
| High risk (T3) | Vertical tumor thickness > 6 mm | 16 % |
PEK staging according to UICC TNM and AJCC 2010.
| Stage | T | N | M |
| 0 | – | – | – |
| I | 1 | 0 | 0 |
| II | 2 | 0 | 0 |
| III | 3 | 0 | 0 |
| 1-3 | 1 | 0 | |
| IV | 1, 2, 3 | 2 | 0 |
| 4 | Any N | 0 | |
| Any T | 3 | 0 | |
| Any T | Any N | 1 |
Legend
- AJCC: “American Joint Committee on Cancer.”
- M: metastasis, N: “node”, T tumor.
- PEK: squamous cell carcinoma.
- UICC: “Union internationale contre le cancer“.
The following variants of squamous cell carcinoma (PEK) of the skin can be distinguished histomorphologically (some of these are reflected in the WHO/ UICC classification):
| Adenosquamous PEK |
| Acantholytic PEK (syn. adenoid or pseudoglandular). |
| Bowen’s carcinoma/ bowenoid differentiated PEK. |
| Desmoplastic PEK |
| Keratoacanthoma-like PEK/ Keratoacanthoma. |
| Lymphoepithelioma-like PEK |
| Pseudovascular PEK (syn. pseudoangiosarcomatous, pseudoangiomatous). |
| Spindle-cell PEK (syn. sarcomatoid). |
| Verrucous PEK (syn. epithelioma cuniculatum). |
