# What makes a skin cancer high risk: the UK feature lists

Source: https://onco.cc/terms/skin-cancer-high-risk-features/  
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## TL;DR

Low risk and high risk are the words that actually decide what happens to a keratinocyte cancer in Britain, more than any stage. One high-risk feature is enough. The lists are short, they are about the tumour and the margin, and a clinician can add clinical features the pathologist cannot see.

## Summary

The UK reporting datasets publish two tables of high-risk pathological features, and in both, any one feature is enough for high-risk status (RCPath G123 and G124).

**Basal cell carcinoma.** Growth pattern: infiltrative, meaning infiltrating, sclerosing or micronodular. Differentiation: basosquamous. Level of invasion: beyond the subcutaneous fat. Depth or thickness: more than 6 mm. Perineural invasion present. Lymphovascular invasion present, for basosquamous tumours. TNM T category T2, T3 or T4. And margins: involved at 0 mm, or not involved but under 1 mm.

**Squamous cell carcinoma.** Subtype: desmoplastic, spindle cell or sarcomatoid, acantholytic or adenosquamous. Grade: poorly differentiated. Perineural invasion present. Lymphovascular invasion present. Thickness over 4 mm. Level of invasion reaching the subcutaneous fat or beyond. TNM pathological stage T2, T3 or T4. And the same margin rule. The dataset records which body named each feature, which is a useful map of where the guidelines disagree: NICE and the British Association of Dermatologists agree on perineural invasion, thickness over 4 mm and involvement of fat; the BAD's own text and table disagree with each other about whether moderately differentiated tumours count, with the table and the NCCN including them and the text, AJCC, SIGN and WHO restricting it to poorly differentiated; the RCPath follows poorly differentiated.

Two things about these lists are easy to miss. First, they are pathological only. The dataset says in terms that a low-risk squamous cell carcinoma on histological criteria may be upgraded to overall high risk once clinical features are added by the clinician or the multidisciplinary team, and the same note appears on the basal cell table. Site, previous radiotherapy, recurrence, immunosuppression and how fast the lesion grew are not on the pathologist's slide. Second, the whole approach is contested from inside. Both datasets conclude that risk stratification is better undertaken by the treating clinician and the skin cancer multidisciplinary team than as a core entry in a histopathology report, partly because the joint RCPath and BAD national audit found that risk status was one of the most frequently omitted core items in skin cancer reports.

The consequence a patient meets is the referral rule. Low-risk basal cell carcinomas can be treated in primary care by appropriately trained and accredited practitioners; everything else goes to secondary care. High-risk basal cell carcinomas with involved margins, patients for Mohs surgery and immunocompromised patients go to the local skin cancer multidisciplinary team; metastatic disease and people with a genetic susceptibility go to the specialist team.

## Fields

- Kind: Term
- Last checked: 2026-09-25
- Also known as: high-risk basal cell carcinoma; high-risk squamous cell carcinoma; high-risk skin cancer; low-risk skin cancer; skin cancer risk stratification; high-risk pathological features; skin cancer MDT referral; involved margin skin cancer; close margin skin cancer

## Notes

- The same feature has two different thresholds depending on what it is being used for, and the UK dataset publishes a table comparing them. For squamous cell carcinoma, thickness over 4 mm makes a tumour high risk for clinical and multidisciplinary team management, while it takes over 6 mm to upstage a T1 or T2 to T3 in the staging system; level of invasion is 'at or beyond the subcutaneous fat' for risk and 'beyond the subcutaneous fat' for staging; and grade, lymphovascular invasion, subtype and margin status count for risk and not at all for staging (RCPath G124, appendix F). The dataset gives this mismatch as one of the reasons risk status caused confusion in practice, noting that 'particular confusion was generated by different risk factors being used for TNM upstaging compared with the tumour itself'. A tumour can therefore be high risk and low stage at the same time without either label being wrong.
- Risk status used to be a core item in the UK report and was removed. The dataset records that the core item 'caused numerous practical and clinical difficulties, reflected in the low level of acceptance and usage identified in the joint BAD-RCPath audit on NMSC', that binary low and high risk 'at times oversimplified a more complex clinicopathological situation', and that it was therefore moved out of the core section. What replaced it is a judgement made by the treating clinician or the skin cancer multidisciplinary team with the clinical facts in front of them. So an absent risk label on a report is the system working as designed, not an omission.
- The British Association of Dermatologists adds the things a slide cannot show. Its 2021 basal cell carcinoma guideline stratifies low against high risk on twelve criteria, of which only about half are pathological: alongside growth pattern, basosquamous differentiation, level of invasion, depth, perineural invasion, pathological T stage and margins, it counts the anatomical area and size together, whether the borders are well or poorly defined, whether the tumour is primary or recurrent, whether the person is immunosuppressed, and whether the site has had radiotherapy before. Its anatomical areas run from area L, the trunk and limbs, through area M, including the cheeks, forehead, scalp and neck, to area H, the mask areas of the face together with the hands, feet, ankles and genitals, where a tumour of any size is high risk. That is why the same 8 mm tumour is low risk on a back and high risk on a nose.
- The margin rule is stricter than most people expect, and it is not the same as an involved margin. A margin that is clear but under 1 millimetre is itself a defined high-risk pathological feature in both datasets. NICE and the national quality surveillance programme do not make a clear margin under 1 mm a mandatory reason for multidisciplinary team referral, and the datasets say the decision is individual or locally agreed, with a low threshold for asking the team. So a letter saying the cancer was completely removed and the case is still going to the team is not a contradiction.
- Counting the features matters as well as having one. The squamous dataset notes that the evidence strongly suggests that the number of high-risk factors present has significant clinical importance, and the greater the number the greater the overall risk. That is the same insight the Brigham and Women's Hospital system is built on, arriving at the same conclusion from the other direction.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Skin_cancer
- 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
- 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
- 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
- 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

## Connected records

- terms: [How skin carcinoma is staged in Britain: UICC TNM, and why it is not the American system](https://onco.cc/terms/tnm-skin-carcinoma/), [Inherited syndromes that cause skin cancer: Gorlin syndrome and xeroderma pigmentosum](https://onco.cc/terms/inherited-skin-cancer-syndromes/), [Mohs surgery](https://onco.cc/terms/mohs-surgery/), [Perineural invasion (PNI)](https://onco.cc/terms/perineural-invasion/), [Resection margins (R0 / R1 / R2)](https://onco.cc/terms/resection-margins/), [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/), [Wide local excision](https://onco.cc/terms/wide-local-excision/)
- technologies: [Multidisciplinary tumour boards](https://onco.cc/technologies/multidisciplinary-tumour-board/)
- 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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