Keratoacanthoma-Like SCC: Risk Classification
Keratoacanthoma-like lesions (also called keratoacanthomatous SCC) are classified as LOW-RISK variants of cutaneous squamous cell carcinoma according to the American Academy of Dermatology guidelines. 1
Risk Classification Based on Histologic Subtype
The AAD guidelines explicitly categorize keratoacanthomatous SCC as a prognostically favorable histologic subtype that should be reported in pathology specimens because this information is clinically useful for risk stratification 1. This designation places it in the low-risk category alongside other favorable variants like verrucous carcinoma 1.
Treatment Implications of Low-Risk Classification
- Standard excision with 4-6 mm margins is recommended for low-risk primary cSCC, which would include keratoacanthoma-like lesions 1
- Curettage and electrodessication (C&E) may be considered for low-risk cSCC in non-terminal hair-bearing locations 1
- Less aggressive surgical approaches are appropriate compared to high-risk tumors, which require Mohs micrographic surgery 1
Important Clinical Context and Caveats
The Ongoing Controversy
There is substantial debate in dermatopathology about whether keratoacanthomas represent:
- A benign, self-limiting tumor distinct from SCC that can spontaneously regress 2, 3, 4
- A well-differentiated variant of SCC with low malignant potential 5, 4
- A borderline lesion between benign and malignant 6
Despite this controversy, the clinical standard is to treat keratoacanthomas surgically because definitive differentiation from well-differentiated SCC is often impossible histologically 2, 4, 7.
Key Distinguishing Features
When keratoacanthoma features are present in an SCC, this typically indicates:
- Lower proliferative activity with fewer dispersed Ki67+ keratinocytes compared to conventional cSCC 8
- Less immunosuppressive tumor microenvironment with fewer regulatory T-cells and different immune cell interactions 8
- Tendency toward regression mediated by immunologic mechanisms 4
- No reported deaths from definitive keratoacanthomas, compared to ~1.5% mortality for cSCC 2
Clinical Pitfall to Avoid
Do not assume all crateriform lesions are keratoacanthomas. Several distinct entities can present with similar crateriform architecture 6:
- True keratoacanthoma (hair follicle-related)
- KA-like SCC (borderline lesion)
- KA with malignant transformation
- Infundibular SCC (crateriform)
- Crateriform SCC arising from actinic keratosis
- Crateriform Bowen's disease
The last two categories are NOT related to hair follicles or true keratoacanthoma and should not be considered low-risk based on architecture alone 6.
Pathology Reporting Requirements
When keratoacanthomatous features are identified, the pathology report should include 1:
- Degree of cellular differentiation
- Depth of invasion in millimeters
- Presence of perineural or lymphovascular invasion
- Margin status
- Specific notation of the keratoacanthomatous subtype as a favorable prognostic feature