The new 8th edition of TNM staging and its implications for skin cancer: a review by the British Association of Dermatologists and the Royal College of Pathologists, United Kingdom
The 8th edition of TNM (Tumour, Node and Metastasis) has numerous and important changes compared to the 7th edition. Public Health England (PHE) and the Royal College of Pathologists, United Kingdom (RCPath) have adopted the 8th edition of TNM (TNM8) published by the Union for International Cancer Control (UICC) for skin cancer staging. These changes will have an impact on the management of both non-melanoma and melanoma skin cancer by all members of the skin cancer multidisciplinary team. These will also need to be highlighted to commissioners and managers for appropriate service planning. T1 to T3 categories for non-melanoma skin cancer (NMSC) staging require the clinician to measure the maximum dimension (usually diameter) of every potential invasive cancer. This measurement must be recorded in the patient record and entered on the histopathology specimen request form. The clinical measurement should be expressed in whole millimetres and a standardised national request form would promote this overall aim. For squamous, basal and adnexal carcinomas, but not Merkel cell carcinoma (MCC), the T1 to T3 categories are defined by new 20 and 40 mm divisions based on the maximum dimension of the lesion. In addition, new risk factors upstage T1 or T2 to T3. These include deep invasion (a tumour depth greater than 6 mm and/or invasion beyond the subcutaneous fat), or specifically defined perineural invasion. Unlike TNM7, tumour site and histological differentiation are not included in TNM8 staging. For melanoma, although ulceration still remains, mitotic index no longer influences separation of pT1 into pT1a and pT1b subdivisions. Instead there is a new additional stratification level at 0.8 mm Breslow thickness. Subdivision pT1b, with a negative sentinel lymph node biopsy (pN0), is now stage IA compared to the previous IB and therefore now has a NICE recommendation for a 1-year rather than 5-year follow-up. The pN subdivisions require information on whether involved lymph nodes are clinically occult or detectable; information that must be recorded clinically and conveyed to the reporting pathologist. For MCC, sentinel lymph node biopsy (SLNB) is now included specifically in the pN staging system. The pT1 subdivision requires clinical information as to whether histologically involved nodes were clinically occult or detectable. This, like the maximum tumour diameter for other NMSC, is clinical information which must be recorded and made available to the reporting pathologist for staging purposes. Eyelid carcinoma continues to have a staging system different from general skin and the system is substantially revised in TNM8. This article is protected by copyright. All rights reserved.
- Oncology 
Slater, David, N