Skin Cancers
Staging
Skin cancers are classified and staged according to the tumor, node and metastasis (TNM) system developed by the American Joint Committee on Cancer (AJCC). Doctors categorize the tumor (T) according to its size and location, whether cancer cells are found in nearby lymph nodes (N) and whether the cancer has metastasized (M), or spread, to other parts of the body. CSCC is also classified by grades, which are different from the stages used to classify most other cancers. Tumor grades are based on how closely the cells resemble normal, healthy cells when viewed under a microscope. The pathologist will examine cells through a microscope and then assign a number to the grade according to how different these cells are from normal tissue cells.
Table 1. AJCC TNM System for Classifying Non-Melanoma Skin Cancer
| Classification | Definition |
| Tumor (T) | |
| Tx | Primary tumor cannot be assessed. |
| Tis | Carcinoma in situ. |
| T1 | Tumor smaller than 2 cm in greatest dimension. |
| T2 | Tumor 2 cm or larger, but smaller than 4 cm in greatest dimension. |
| T3 | Tumor 4 cm or larger in maximum dimension or minor bone erosion or perineural invasion or deep invasion. |
|
T4
T4a T4b |
Tumor with gross cortical bone/marrow, skull base invasion and/or skull base foramen invasion.
Tumor with gross cortical bone/marrow invasion. Tumor with skull base invasion and/or skull base foramen involvement. |
| Node (N) | |
| Nx | Regional lymph nodes cannot be assessed. |
| N0 | No regional lymph node metastasis. |
| N1 |
Metastasis in a single ipsilateral lymph node, 3 cm or smaller in greatest dimension and ENE**(+);
or larger than 3 cm but not larger than 6 cm in greatest dimension and ENE(–); or metastases in multiple ipsilateral (on the same side of the body) lymph nodes, none larger than 6 cm in greatest dimension and ENE(–); or in bilateral (on both sides of the body) or contralateral (on the opposite side of the body) lymph node(s), none larger than 6 cm in greatest dimension, ENE(–). |
|
N2a
N2b N2c |
Metastasis in single ipsilateral (on the same side of the body) node 3 cm or smaller in greatest dimension and ENE**(+);
or a single ipsilateral node larger than 3 cm but not larger than 6 cm in greatest dimension and ENE(–). Metastasis in multiple ipsilateral (on the same side of the body) nodes, none larger than 6 cm in greatest dimension and ENE**(–). Metastasis in bilateral (on both sides of the body) or contralateral (on the opposite side of the body) lymph node(s), none larger than 6 cm in greatest dimension and ENE(–). |
|
N3
N3a N3b |
Metastasis in a lymph node larger than 6 cm in greatest dimension and ENE**(–);
or in a single ipsilateral (on the same side of the body) node larger than 3 cm in greatest dimension and ENE(+); or multiple ipsilateral, contralateral (on the opposite side of the body), or bilateral (on both sides of the body) nodes, any with ENE(+); or a single contralateral (on the opposite side of the body) node 3 cm or smaller and ENE(+). Metastasis in a lymph node larger than 6 cm in greatest dimension and ENE**(–). Metastasis in a single ipsilateral (on the same side of the body) node larger than 3 cm in greatest dimension and ENE**(+); or multiple ipsilateral, contralateral (on the opposite side of the body), or bilateral (on both sides of the body) nodes, any with ENE(+); or a single contralateral (on the opposite side of the body) node 3 cm or smaller and ENE(+). |
|
Note: A designation of “U” or “L” may be used for any N category to indicate metastasis above the lower border of the cricoid (U) or below the lower border of the cricoid (L).
**Extranodal extension (ENE) refers to cancer cells that have spread through the node into surrounding connective tissue. |
|
| Metastasis ( M) | |
| M0 | No distant metastasis. |
| M1 | Distant metastasis. |
Table 2. Stages of Non-Melanoma Skin Cancer
| Stage | T | N | M |
| 0 | Tis | N0 | M0 |
| I | T1 | N0 | M0 |
| II | T2 | N0 | M0 |
| III |
T3
T1 - T3 |
N0
N0 |
M0
M0 |
| IV |
T1-T3
Any T T4 Anyh T |
N2
N3 Any N Any N |
M0
M0 M0 M1 |
Table 3. Stages of Non-Melanoma Skin Cancer
| Classification | Definition |
| GX | Grade cannot be assessed. |
| G1 | Well differentiated. |
| G2 | Moderately differentiated. |
| G3 | Poorly differentiated. |
| G4 | Undifferentiated. |
Stages of Non-Melanoma Skin Cancer
Table 4. AJCC TNM System for Classifying Merkel Cell Carcinoma (MCC)
| Classification | Definition |
| Tumor (T) | |
| Tx | Primary tumor cannot be assessed (e.g., curetted). |
| T0 | No evidence of primary tumor. |
| Tis | In situ primary tumor. |
| T1 | Maximum clinical tumor diameter < 2 cm (or less). |
| T2 | Maximum clinical tumor diameter > (more than) 2 cm but ≯ (not more than) 5 cm. |
| T3 | Maximum clinical tumor diameter > (more than) 5 cm. |
| T4 | Primary tumor invades fascia, muscle, cartilage, or bone. |
| Node (N) | |
| Nx | Regional lymph nodes cannot be assessed. |
| N0 | No regional lymph node metastasis detected on pathological evaluation. |
|
N1
N1a(sn) N1a N1b |
Metastasis in regional lymph node(s).
Clinically occult regional lymph node metastasis identified only by sentinel lymph node biopsy. Clinically occult regional lymph node metastasis following lymph node dissection. Clinically and/or radiologically detected regional lymph node metastasis, microscopically confirmed. |
| N2 | In-transit metastasis (discontinuous from primary tumor; located between primary tumor and draining regional nodal basin, or distal to the primary tumor) without lymph node metastasis. |
| N3 | In-transit metastasis (discontinuous from primary tumor; located between primary tumor and draining regional nodal basin, or distal to the primary tumor) with lymph node metastasis. |
| Metastasis ( M) | |
| M0 | No distant metastasis detected on clinical and/or radiologic examination. |
|
M1
M1a M1b M1c |
Distant metastasis microscopically confirmed.
Metastasis to distant skin, distant subcutaneous tissue, or distant lymph node(s), microscopically confirmed. Metastasis to lung, microscopically confirmed. Metastasis to all other distant sites, microscopically confirmed. |
Table 5. Stages of Merkel Cell Carcinoma (MCC)
| Stage | T | N | M |
| 0 | Tis | N0 | M0 |
| I | T1 | N0 | M0 |
| IIA | T2-3 | N0 | |
| IIB | T4 | N0 | M0 |
| IIIA |
T1-4
T0 |
N1a(sn) or
N1a N1b |
M0
M0 |
| IIIB | T1-4 | N1b-3 | M0 |
| IV | T0-4 | Any N | M1 |
Used with permission of the American Joint Committee on Cancer (AJCC), Chicago, Illinois. The original and primary source for this information is the AJCC Cancer Staging Manual, Eighth Edition (2017) published by Springer Science+Business Media.
Stages of Merkel Cell Carcinoma (MCC)
