Keratoacanthoma

Section: Skin and soft tissue Sub-section: Skin cancer Curriculum: Curriculum, page 52

Definition

• Benign , rapidly growing, locally destructive overgrowth of hair follicle cells
  • May regress spontaneously with scarring
• Arises from the infundibulum of the hair follicle

Risk

• Sun exposure
• Age
• Male
• Genetic
  • Xeroderma Pigmentosum
  • Muir-Torre syndrome
  • Multiple self-healing squamous epithelioma (Ferguson-Smith syndrome)
  • Eruptive keratoacanthoma of Grzybowski
  • Incontinentia pigmenti

Clinical

• Solitary, rapidly growing nodule on sun-exposed skin of the face and upper limbs.
• Sharply demarcated, firm, erythematous or skin-coloured, with a classic central hyperkeratotic plug and an even shoulder.
  • Removal of the keratotic core will leave a ‘crater’-like appearance to the lesion.
• 3 clinical phases:
  • proliferative, maturation & involution
    • Grows rapidly (2-4wks) as a ‘volcano’ / cone-shape (flesh coloured) with a dense keratin plug in its ‘crater’
    • Then spontaneously regresses (over 2-3mths) → Leaves a deep, puckered scar

Pathology

• KA arises from the pilosebaceous unit, particularly the hair follicle epithelium. It is considered a well-differentiated squamous neoplasm

Differential diagnosis

• SCC
  • May be well-differentiated variants of SCC capable of spontaneous regression
• Difficult to distinguish from SCC histologically
  • Usually no atypia & sharply demarcated, with an epithelial lip
  • Compared to SCC – many mitotic figures, ulcerated

Investigations:

• Excision biopsy

Management

• Clinically they may be indistinguishable from well-differentiated squamous cell carcinoma
  • Thus, many clinicians and pathologists prefer the term SCC, KA-type and recommend surgical excision
• Surgical management is usually preferred
  • Unless there is clear evidence that regression is in progress.