# How skin carcinoma is staged in Britain: UICC TNM, and why it is not the American system

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## TL;DR

UK skin carcinoma reports are staged against the UICC's system, not the American AJCC's, and the two are not the same: the American manual covers only the head and neck, while the UICC covers the whole body and includes basal cell carcinoma. In practice almost no basal cell carcinoma is ever given a stage, because the stage would not change anything.

## Summary

**Which system, and why.** The Royal College of Pathologists assessed both and chose UICC, noting that UICC TNM 'is the version favoured by NCRAS in the UK' and that the decision between the two rested on the staging of non-melanoma skin cancer, because for melanoma and Merkel cell carcinoma the two are now identical (G123). The difference is one of coverage. The AJCC eighth edition has a chapter on cutaneous squamous cell carcinoma of the head and neck, which also takes in basal cell and adnexal carcinoma but not Merkel cell carcinoma, and it has no staging system for squamous cell carcinoma anywhere else on the body. The UICC has both a head-and-neck chapter and a separate carcinoma-of-the-skin chapter for the rest, essentially trunk and limbs but excluding the eyelid, vulva, penis and perianal skin. The boundary between the two regions is the acromioclavicular joint in front and the upper margin of the shoulder blade behind. A further small discrepancy has never been resolved: UICC divides the size categories at 20 mm or less, over 20 to 40 mm and over 40 mm, while AJCC divides at under 20 mm, 20 to under 40 mm and 40 mm or more, and the RCPath judged the UICC breakpoints more likely to be correct because they match the ones both bodies use for Merkel cell carcinoma and lip and oral cavity tumours.

**The categories, in the ninth edition now in force.** pTis is carcinoma in situ. pT1 is 20 mm or less in maximum dimension, pT2 over 20 up to 40 mm, pT3 over 40 mm; pT3 is also reached by minor bone erosion, by perineural invasion or by deep invasion, whatever the size. Deep invasion means invasion beyond the subcutaneous fat, or more than 6 mm measured from the granular layer of adjacent normal epidermis to the base of the tumour. Perineural invasion means tumour within the nerve sheath of a nerve lying deeper than the dermis, or measuring 0.1 mm or more in calibre, or involvement of five or more nerves in a section, short of foramen or skull base involvement. pT4a is gross cortical or marrow invasion and pT4b is axial skeleton invasion including the vertebral foramen and epidural space. Nodal categories differ between the two body regions: for trunk and limbs they run on ipsilateral node size alone, 30 mm and 60 mm, and a contralateral node counts as distant metastasis; for head and neck they are subdivided by extranodal extension as well. The stage groups are simple: stage 0 is Tis, stage I is T1N0, stage II is T2N0, stage III is T3N0 or any of T1 to T3 with N1, stage IV is anything more.

**Why almost nobody is told a stage.** Cancer Research UK puts it plainly: most basal cell carcinomas do not need staging because it is very rare for them to spread, and staging is more likely with a squamous cell carcinoma because those can spread, although that is still rare. So the odd position in Britain is that basal cell carcinoma is formally stageable, with its own UICC appendix in the national reporting dataset, and is almost never staged; while in the United States there is no system for it outside the head and neck at all. Neither country routinely gives a person with a basal cell carcinoma a stage number, and a reader who cannot find one on their letter has not been overlooked.

## Fields

- Kind: Term
- Last checked: 2026-09-25
- Also known as: TNM skin carcinoma; UICC TNM 9 skin; UICC TNM 8 skin; skin cancer staging; carcinoma of the skin staging; skin carcinoma of the head and neck; AJCC 8 cutaneous squamous cell carcinoma; pT1 skin; pT2 skin; pT3 skin; pT4a skin; pT4b skin; basal cell carcinoma staging; cSCC staging; deep invasion skin; stage 0 skin cancer

## Notes

- The British guidelines say the same thing as the pathologists, in their own words. The British Association of Dermatologists' 2020 cutaneous squamous cell carcinoma guideline states that the guideline development group adopted the Royal College of Pathologists dataset, and that this, along with Public Health England, endorses the UICC eighth edition rather than the AJCC eighth edition, noting that AJCC 8 covers only head and neck disease. The 2021 basal cell carcinoma guideline says it adapted the American NCCN criteria 'to equate to the UICC8 and RCPath dataset' because the UICC version 'has been endorsed for use in the UK'. Both also note that the eyelid has been excluded from skin carcinoma staging for several editions and has a staging system of its own.
- The American system has not been revised for skin, which is why the comparison is still with the eighth edition. The AJCC is issuing its ninth edition site by site rather than as a book, and states that all disease sites in the eighth edition remain current until replaced. Cervix, appendix, anus, brain and spinal cord, seven neuroendocrine and gynaecological sites, lung, thymus, pleural mesothelioma, nasopharynx, salivary glands and HPV-associated oropharynx have been released; cutaneous carcinoma has not. So an American source citing AJCC 8 for skin in 2026 is citing the current American system, while a British report citing UICC TNM 9 is citing a newer one.
- What the eighth edition changed, and why it mattered here more than elsewhere. The joint review by the British Association of Dermatologists and the Royal College of Pathologists set it out: the T1 to T3 categories for non-melanoma skin cancer were redefined around new 20 mm and 40 mm divisions, and new risk factors can upstage T1 or T2 to T3. That review states that Public Health England and the Royal College of Pathologists adopted UICC TNM 8 for skin cancer staging, and warns that the change would affect the management and commissioning of both melanoma and non-melanoma skin cancer (Keohane 2018). Before it, in the seventh edition, most squamous cell carcinomas fell into T2 and T3 and T4 cases were rare, which is the problem the next term is about.
- What the ninth edition changed. The perineural invasion definition now includes involvement of five or more nerves in a section alongside the nerve-calibre and nerve-depth criteria, and UICC states that pT is identical to T. The UK appendix carrying the ninth edition for skin carcinoma is dated 6 November 2025 and combines the head-and-neck and carcinoma-of-the-skin chapters into one table, covering basal cell, squamous cell and adnexal carcinoma but excluding Merkel cell carcinoma and carcinomas of the eyelid, vulva, penis, non-hair-bearing lip and non-hair-bearing perianal skin.
- The size on the report may be a clinical measurement rather than a microscopic one. Both bodies prefer the clinical maximum dimension and allow a pathological one if no clinical measurement is available, and the UK dataset added an item recording which was used. This is worth knowing because it means a difference of a millimetre either side of 20 mm can be a difference of measuring technique rather than of tumour.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/TNM_staging_system
- Royal College of Pathologists appendix A, version 3, 6 November 2025: UICC TNM 9 pathological staging of primary cutaneous carcinoma (basal cell), combining the UICC chapters for skin carcinoma of the head and neck and carcinoma of the skin: https://www.rcpath.org/resourceLibrary/basal-cell-tnm9.html
- Royal College of Pathologists appendix A: UICC TNM 9 pathological staging of primary cutaneous carcinoma (squamous cell): https://www.rcpath.org/resourceLibrary/squamous-cell-tnm9.html
- Royal College of Pathologists G123: dataset for histopathological reporting of primary cutaneous basal cell carcinoma, version 4, February 2019 (Slater and Barrett): https://www.rcpath.org/resourceLibrary/g123-dataset-basal.html
- Royal College of Pathologists G124: dataset for histopathological reporting of primary invasive cutaneous squamous cell carcinoma and regional lymph nodes, version 4, February 2019 (Slater and Barrett): https://www.rcpath.org/resourceLibrary/g124datasetsquamous-pdf.html
- Keohane, Proby, Newlands, Motley, Nasr and Mohd Mustapa, British Journal of Dermatology 2018;179:824 to 828: 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, UK: https://doi.org/10.1111/bjd.16892
- Cancer Research UK: stages and grades of non-melanoma skin cancer: https://www.cancerresearchuk.org/about-cancer/skin-cancer/stages-grades
- American College of Surgeons: AJCC Version 9 cancer staging system (all 8th edition disease sites remain current until replaced; no cutaneous carcinoma version 9 protocol has been released): https://www.facs.org/quality-programs/cancer-programs/american-joint-committee-on-cancer/version-9/
- Royal College of Pathologists: cancer datasets and tissue pathways index (the skin datasets G123 and G124 are listed as currently on hold; their UICC TNM 9 appendices were published in November 2025 and their SNOMED appendices updated in February 2026): https://www.rcpath.org/profession/guidelines/cancer-datasets-and-tissue-pathways.html
- Keohane et al., British Journal of Dermatology 2021;184(3):401 to 414: British Association of Dermatologists guidelines for the management of people with cutaneous squamous cell carcinoma 2020: https://doi.org/10.1111/bjd.19621
- Nasr et al., British Journal of Dermatology 2021;185(5):899 to 920: British Association of Dermatologists guidelines for the management of adults with basal cell carcinoma 2021: https://doi.org/10.1111/bjd.20524

## Connected records

- terms: [AJCC stage (TNM staging manual)](https://onco.cc/terms/ajcc-stage/), [Extranodal extension (ENE)](https://onco.cc/terms/extranodal-extension/), [Keratinocyte cancer (and why 'non-melanoma skin cancer' is being retired)](https://onco.cc/terms/keratinocyte-cancer/), [Perineural invasion (PNI)](https://onco.cc/terms/perineural-invasion/), [Stage](https://onco.cc/terms/cancer-stage/), [The Brigham and Women's Hospital staging system, and why squamous cell carcinoma has two](https://onco.cc/terms/bwh-staging-cscc/), [The growth pattern on a basal cell carcinoma report: nodular, superficial, infiltrative, basosquamous](https://onco.cc/terms/bcc-growth-pattern/), [The subtype and grade on a cutaneous squamous cell carcinoma report](https://onco.cc/terms/cscc-subtype-and-grade/), [TNM staging](https://onco.cc/terms/tnm-staging/), [What makes a skin cancer high risk: the UK feature lists](https://onco.cc/terms/skin-cancer-high-risk-features/)
- cancers: [Advanced cutaneous squamous cell carcinoma](https://onco.cc/cancers/advanced-cutaneous-scc/), [Basal cell carcinoma](https://onco.cc/cancers/basal-cell-carcinoma/), [Bowen's disease (squamous cell carcinoma in situ)](https://onco.cc/cancers/bowens-disease/), [Cutaneous squamous cell carcinoma](https://onco.cc/cancers/cutaneous-scc/), [Locally advanced and metastatic basal cell carcinoma](https://onco.cc/cancers/locally-advanced-bcc/), [Merkel cell carcinoma](https://onco.cc/cancers/merkel-cell-carcinoma/), [Skin cancer (all types)](https://onco.cc/cancers/skin-cancer/)
- fronts: [Diagnostics & Biomarkers](https://onco.cc/fronts/diagnostics/)

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