CARCINOMA OF THE SKIN (EXCLUDING EYELID, HEAD AND NECK, PERIANAL, VULVA, AND PENIS) (ICD‐O‐3 C44.5–7, C63.2)

Rules for Classification

The classification applies only to carcinomas, excluding Merkel cell carcinoma. There should be histological confirmation of the disease and division of cases by histological type.

Regional Lymph Nodes

The regional lymph nodes are those appropriate to the site of the primary tumour. See Regional Lymph Nodes under Skin Tumours.

TNM Clinical Classification

T – Primary Tumour

TX	Primary tumour cannot be assessed
T0	No evidence of primary tumour
Tis	Carcinoma in situ (Fig. 329)
T1	Tumour 2 cm or less in greatest dimension (Fig. 330)
T2	Tumour > 2 cm and ≤ 4 cm in greatest dimension (Fig. 331)
T3	Tumour > 4 cm in maximum dimension or minor bone erosion or perineural invasion or deep invasion* (Fig. 332)
T4a	Tumour with gross cortical bone/ marrow invasion,
T4b	Tumour with axial skeleton invasion including foraminal involvement and/or vertebral foramen involvement to the epidural space.

*Deep invasion is defined as invasion beyond the subcutaneous fat or > 6 mm (as measured from the granular layer of adjacent normal epidermis to the base of the tumour), perineural invasion for T3 classification is defined as clinical or radiographic involvement of named nerves without foramen or skull base invasion or transgression.

Schematic illustration of Carcinoma in situ. — **Fig. 329**

Schematic illustration of tumour 2 cm or less in greatest dimension. — **Fig. 330**

Schematic illustration of tumour greater than 2 cm and less than or equal to 4 cm in greatest dimension. — **Fig. 331**

NoteIn the case of multiple simultaneous tumours, the tumour with the highest T category is classified and the number of separate tumours is indicated in parentheses, e.g., T2(5) (Fig. 333)

Schematic illustration of tumour greater than 4 cm in maximum dimension or minor bone erosion or perineural invasion or deep invasion. — **Fig. 332**

Schematic illustration of tumour with the highest T category is classified and the number of separate tumours is indicated in parentheses. — **Fig. 333**

N – Regional Lymph Nodes

NX	Regional lymph nodes cannot be assessed
N0	No regional lymph node metastasis
N1	Metastasis in a single ipsilateral lymph node, 3 cm or less in greatest dimension
N2	Metastasis in a single ipsilateral lymph node, more than 3 cm but not more than 6 cm in greatest dimension, or in multiple ipsilateral lymph nodes, none more than 6 cm in greatest dimension, or in bilateral or contralateral lymph nodes, none more than 6 cm in greatest dimension
N3	Metastasis in a lymph node, more than 6 cm in greatest dimension

M – Distant Metastasis

M0	No distant metastasis
M1	Distant metastasis (Figs. 324, 325, 326, 327, 328)

pTNM Pathological Classification

The pT, and pN categories correspond to the T and N categories.

pM1	Distant metastasis microscopically confirmed

NotepM0 and pMX are not valid categories.

pN0

Histological examination of a regional lymphadenectomy specimen will ordinarily include 6 or more lymph nodes. If the lymph nodes are negative, but the number ordinarily examined is not met, classify as pN0.