Skin nonmelanocytic tumor
Carcinoma (nonadnexal)

Topic Completed: 1 June 2012

Minor changes: 27 November 2020

Copyright: 2002-2021,, Inc.

PubMed Search: Keratoacanthoma [title]

Christopher S. Hale, M.D.
Page views in 2020: 25,824
Page views in 2021 to date: 1,599
Cite this page: Hale CS. Keratoacanthoma. website. Accessed January 22nd, 2021.
Definition / general
  • Considered by some to be squamous cell carcinoma, acanthomatous type
  • May represent proliferation of infundibular portion of hair follicle (since keratinization occurs without a granular cell layer), or a subtype of well differentiated squamous cell carcinoma
Clinical features
  • 80% males, usually sun exposed skin of face
  • Also associated with inflammatory dermatoses, congenital lesions, genetic diseases, scars
  • Younger age group than squamous cell carcinoma of skin
  • Familial cases may be multiple
  • Usually arises from normal skin, grows rapidly for 4 - 8 weeks, then regresses over 6 months to leave a depressed, annular scar
  • Rarely metastasizes, usually in immunosuppressed patients
  • Gryzbowski type: numerous eruptive lesions
  • Ferguson-Smith type: multiple ulcerating tumors with atypical distribution
  • Subungual keratoacanthoma: may arise from nail matrix; rapidly growing mass in tip of finger or toe; associated with lytic, cup shaped defect of distal digit
Case reports
Clinical images

Images hosted on other servers:

Before and after
topical treatment
with 5% potassium
dobesilate cream

Gross description
  • Flesh colored, dome shaped lesion with central, keratin-filled crater
Microscopic (histologic) description
Early (evolving) phase:
  • Composed of well circumscribed solid lobules of large, pale squamous cells with little keratinization
  • Distorted follicular infundibulum
  • Mild atypia

Stable phase:
  • Has central crater filled with keratin but no granular layer
  • Larger more irregular infiltrating squamous nests and islands, accompanied by marked inflammatory infiltrate with lichenoid features and eosinophils but no plasma cells
  • May be deeply infiltrative, with microabscesses of neutrophils and eosinophils approaching surface
  • Often marked atypia, mitotic figures, atypical mitotic figures at periphery, perineural invasion, rarely vascular invasion

Regressing (resolving) phase:
  • Has keratin filled crater, mature epithelium without atypia
  • Flattening of cup-shape, horizontal fibrosis in dermis
  • Reduction of inflammation, transdermal elimination of elastic fibers
  • Note: overhanging edges, keratin-filled crater and hemispheric shape are most important features in differentiating from squamous cell carcinoma

  • Actinic-arises from actinic keratosis and has marked atypia
  • Follicular-plaque with numerous vertical strands of squamous epithelium resembling keratoacanthoma
  • Giant-10-15 cm, may cover most of a member
Microscopic (histologic) images

Contributed by Andrey Bychkov, M.D., Ph.D.

Central crater

No granular layer

Images hosted on other servers:


Negative stains
  • p53 (usually)
Molecular / cytogenetics description
Differential diagnosis
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