# Keratoacanthoma: the tumour that may be a squamous cell carcinoma

Source: https://onco.cc/terms/keratoacanthoma/  
OnCo record `keratoacanthoma` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A dome-shaped lump with a central plug of keratin that grows fast over a few weeks and may then shrink on its own. Whether it is a benign tumour or a squamous cell carcinoma that happens to regress has been argued for decades; the WHO treats it as a type of squamous cell carcinoma, and no single test tells them apart.

## Summary

No question in skin pathology has been reopened as often. The fourth edition of the WHO skin classification (2018) placed keratoacanthoma inside the squamous cell carcinoma section, and the UK reporting dataset recorded that position in terms: it notes the WHO terminology, which considers keratoacanthoma as synonymous with invasive squamous cell carcinoma of keratoacanthomatous type; it notes that there is still considerable national and international debate as to whether keratoacanthoma is truly a pathologically benign or malignant neoplasm; and it records that, to date, no one single criterion can make a reliable distinction between squamous cell carcinoma and keratoacanthoma, so each case must be approached using a constellation of clinical and pathological features, including a history of an initial period of rapid growth (RCPath G124). The fifth edition (2025) then moved it back out, making it a heading of its own beside the basal cell and squamous cell carcinomas, while conceding the same difficulty: reliable distinction between the two is not always possible, immunohistochemistry for p53, Ki-67 and p16 helps in many cases, and where it does not, the uncertainty can be reported as a squamoproliferative tumour of uncertain malignant potential.

The coding follows the confusion rather than resolving it. ICD-O-3.2 carries keratoacanthoma as a related term under 8071/3, squamous cell carcinoma, keratinizing, which is a malignant behaviour code. The UK dataset's own coding appendix does the opposite, coding keratoacanthoma as SNOMED M7286/0, a benign behaviour code, and keeping keratoacanthoma-like squamous cell carcinoma separately at M8071/3. A British pathologist reporting the same lesion under the two systems would file it as benign in one and malignant in the other.

The same dataset adds a safety rule that is the practical point for a reader. The term keratoacanthoma should perhaps be avoided in an immunosuppressed patient, and for large lesions, and in a subungual location under a nail, because all of those are considered to have greater potential for aggressive behaviour. In other words, the cases where calling it a keratoacanthoma would be most reassuring are the cases where it is least safe to.

This is why keratoacanthoma is a word here and not a page. The corpus gives a page to a lesion with a settled behaviour that registries register; this one has neither, and its position in the reference classification has moved in both directions within seven years. Anyone whose biopsy report carries the word should read the cutaneous squamous cell carcinoma page, which is where the management of the thing in front of them is written.

## Fields

- Kind: Term
- Last checked: 2026-09-25
- Also known as: keratoacanthoma; KA; squamous cell carcinoma keratoacanthoma type; keratoacanthomatous squamous cell carcinoma; self-healing squamous carcinoma

## Notes

- Why spontaneous regression is not a reason to wait. The natural history that gave keratoacanthoma its reputation, rapid growth then involution, is exactly what makes it indistinguishable in advance from a squamous cell carcinoma that will not involute. Since no single criterion separates them and the diagnosis is made on the whole picture rather than one feature, the safe path is to treat the lesion and let the pathology decide afterwards.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Keratoacanthoma
- 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
- Cancer Research UK: squamous cell carcinoma of the skin: https://www.cancerresearchuk.org/about-cancer/skin-cancer/types/squamous-cell-carcinoma
- WHO Classification of Tumours Editorial Board: Skin tumours, 5th edition, volume 12 (IARC, Lyon, 2025), ISBN 978-92-832-4535-3: https://publications.iarc.who.int/Book-And-Report-Series/Who-Classification-Of-Tumours/Skin-Tumours-2025
- Elder, Massi, Scolyer and Willemze (eds): WHO Classification of Skin Tumours, 4th edition, volume 11 (IARC, Lyon, 2018): https://publications.iarc.who.int/Book-And-Report-Series/Who-Classification-Of-Tumours/WHO-Classification-Of-Skin-Tumours-2018
- Histopathology 2026;88:555 to 568: WHO classification of skin tumours, key updates in the fifth edition (open-access summary of what the 2025 volume changed): https://doi.org/10.1111/his.15562
- IARC and the International Association of Cancer Registries: ICD-O-3.2 morphology and behaviour codes (actinic keratosis 8070/0; Bowen disease 8081/2; keratoacanthoma a related term under 8071/3; micronodular basal cell carcinoma shares 8097/3 with nodular, and sclerosing or morphoeic shares 8092/3 with infiltrating): http://www.iacr.com.fr/index.php?option=com_content&view=category&layout=blog&id=100&Itemid=577

## Connected records

- terms: [Actinic keratosis (solar keratosis): sun damage, not cancer](https://onco.cc/terms/actinic-keratosis/), [Histology](https://onco.cc/terms/histology/), [Keratinocyte cancer (and why 'non-melanoma skin cancer' is being retired)](https://onco.cc/terms/keratinocyte-cancer/), [Squamous cell carcinoma](https://onco.cc/terms/squamous-cell-carcinoma/), [The subtype and grade on a cutaneous squamous cell carcinoma report](https://onco.cc/terms/cscc-subtype-and-grade/), [Tumour differentiation (well / moderately / poorly differentiated)](https://onco.cc/terms/tumour-differentiation/)
- cancers: [Bowen's disease (squamous cell carcinoma in situ)](https://onco.cc/cancers/bowens-disease/), [Cutaneous squamous cell carcinoma](https://onco.cc/cancers/cutaneous-scc/), [Skin cancer (all types)](https://onco.cc/cancers/skin-cancer/)
- fronts: [Diagnostics & Biomarkers](https://onco.cc/fronts/diagnostics/)

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