Skin nonmelanocytic tumor
Carcinoma (nonadnexal)
Keratoacanthoma

Editor-in-Chief: Debra L. Zynger, M.D.
Mary Dick, M.D.
Poonam Sharma, M.B.B.S.

Minor changes: 15 April 2021

Copyright: 2002-2021, PathologyOutlines.com, Inc.

PubMed Search: Keratoacanthoma[title] skin "free full text"[sb]

Mary Dick, M.D.
Poonam Sharma, M.B.B.S.
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Cite this page: Dick M, Sharma P. Keratoacanthoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumornonmelanocytickeratoacanthoma.html. Accessed May 8th, 2021.
Definition / general
  • Keratoacanthoma (KA) is a well differentiated, cutaneous squamous cell carcinoma, which often spontaneously regresses
  • Regression is thought to be due to immune mediated destruction of squamous cells
  • For lesions that are entirely resected, can diagnose as "well differentiated squamous cell carcinoma, keratoacanthoma type”
  • For lesions that are not entirely histologically examined, can diagnose as "well differentiated squamous cell carcinoma with features of keratoacanthoma”
Essential features
  • Common, represents approximately up to 30% of cases of cutaneous squamous cell carcinoma (SCC)
  • Dome shaped tumor with central keratinous plug in sun exposed areas
  • May become large, up to 10 cm (called giant KA)
  • Good prognosis; vast majority of cases spontaneously regress
Terminology
  • Agglomerate KA (variant)
  • KA centrifugum (variant)
  • Giant KA (variant)
  • Subungual KA (variant)
  • Intraoral KA (variant)
ICD coding
  • ICD-O: 8071/3 - keratoacanthoma, NOS
  • ICD-10: L85.8 - other specified epidermal thickening
  • ICD-11: 2F72 - neoplasms of uncertain behavior of skin
Epidemiology
Sites
Pathophysiology
Clinical features
Diagnosis
  • Excisional biopsy preferred to show suggestive histopathology
Prognostic factors
  • Nonfatal tumor
  • Can regress; however, final size prior to regression is difficult to predict (J Am Acad Dermatol 2016;74:1220)
  • Recurrence is uncommon with surgical removal
  • Self limited proliferation with low probability of malignant transformation (more often associated with perineural invasion) (Acta Biomed 2019;90:580)
Case reports
Treatment
  • Monitoring for spontaneous regression; often leaves atrophic hypopigmented scar (Indian J Dermatol 2011;56:435)
  • Typically treated with complete surgical excision; Mohs surgery performed dependent on location (Ann Dermatol 2011;23:357)
  • Electrosurgery, cryosurgery, laser surgery, systemic or topical chemotherapy occasionally utilized (J Dent (Shiraz) 2014;15:91)
  • Radiotherapy can be utilized with reoccurrence or potential large cosmetic disfigurement with surgery; typically not utilized in young adult patients (J Am Acad Dermatol 1990;23:489)
Clinical images

Images hosted on other servers:

Large face tumor

Palm tumor

Forehead lesion

Gross description
  • Typically large, scaly, dome shaped tumor with central keratinous plug
Microscopic (histologic) description
  • Low power magnification shows large, well differentiated squamous tumor with central keratin filled crater
  • Surrounding epidermis forms a lip around the invaginating crateriform tumor
  • Tumor is composed of bland squamous cells with abundant eosinophilic or glassy cytoplasm and enlarged hyperchromatic to vesicular appearing nuclei
  • Mitotic activity and cellular atypia are usually seen at the periphery of tumor
  • Intraepidermal neutrophilic microabscesses and keratin horn pearls are seen within the tumor
  • Regressing tumors show epidermal atrophy, bland cytologic features, dermal inflammation and fibrosis at the periphery of tumor
Microscopic (histologic) images

Contributed by Poonam Sharma, M.B.B.S.

Central crater

Bland squamous cells

Whorl of laminated keratin

Virtual slides

Images hosted on other servers:

Invaginated, keratin filled tumor

Positive stains
Negative stains
Molecular / cytogenetics description
  • Transforming growth factor beta receptor 1 can cause multiple self healing squamous epithelioma (MMSE); most common cause of multiple KA
  • Germline mutations of hMSH2 and hMLH1 mismatch repair genes causing Muir-Torre syndrome have been implicated in solitary and multiple KA formation
  • BRAF kinase inhibitors utilized to treat KA has been reported to induce reactive KA by paradoxical activation of the ERK MAPkinase pathway
  • Reference: Exp Dermatol 2016;25:85
Videos

Keratoacanthoma

Sample pathology report
  • Skin, left cheek (clinical keratoacanthoma), excision:
    • Well differentiated squamous cell carcinoma, keratoacanthoma type (see comment)
    • Comment: Well differentiated hyperplastic squamous epithelium with crater-like depression with keratin horn pearls present centrally. Enlarged hyperchromatic vesicular nuclei present along with glassy appearing cytoplasm.
Differential diagnosis
  • Conventional, well differentiated squamous cell carcinoma:
    • Shows greater cellular atypia and mitotic activity
    • Intraepidermal neutrophilic microabscesses and tissue eosinophilia less common
    • May be difficult to distinguish in superficial biopsies
  • Verrucous carcinoma:
    • Shows prominent endophytic and exophytic growth
    • Lacks central crateriform architecture
    • Also has bland cytologic features
    • May be difficult to distinguish in superficial biopsies
Board review style question #1

A 62 year old man presents with a single, solitary, skin colored tumor that has a crater-like appearance with central keratin buildup on his left forearm. It appeared spontaneously and has grown rapidly over the past 3 weeks. It is painless to the touch but is cosmetically displeasing. He has no other skin conditions. The tumor is excised and a microscopic image is shown above. Which of the following is true concerning this skin lesion?

  1. It is a variant of basal cell carcinoma
  2. The underlying cause for this tumor is typically due to a genetic mutation
  3. The malignant potential of this tumor is high and it must be removed immediately
  4. This tumor has the potential to completely spontaneously regress
Board review style answer #1
D. This tumor has the potential to completely spontaneously regress. This is a well differentiated squamous cell carcinoma, keratoacanthoma type.

Comment Here

Reference: Keratoacanthoma
Board review style question #2
A 70 year old male farmer presents with a skin tumor on his cheek that has grown quickly over the past month. It has a crater-like appearance without arborizing telangiectasias on dermatoscopy. Biopsy shows that the tumor is mainly composed of bland squamous cells with intraepidermal neutrophilic microabscesses and keratin horn pearls under the microscope. Which of the following is true concerning this skin tumor?

  1. Peripheral palisading and clefting are also likely to be seen under the microscope
  2. It has overlapping features of squamous cell carcinoma
  3. Due to its rapid growth, this tumor is likely to metastasize
  4. Excessive UV damage plays no role in pathogenesis
Board review style answer #2
B. It has overlapping features of squamous cell carcinoma. The lesion is a keratoacanthoma.

Comment Here

Reference: Keratoacanthoma
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