II. Epidemiology

  1. Onset later in life

III. Pathophysiology

  1. Squamoproliferative, benign epithelial lesions
  2. No longer thought to be associated with malignancy
    1. Not a squamous cell cancer variant
    2. May be difficult to distinguish from SCC (see below)

IV. Risk Factors

  1. Ultraviolet light exposure
  2. Human Papillomavirus
  3. Coal tar derivative exposure
  4. Cigarette smoking
  5. Chemical carcinogens

V. Signs

  1. Characteristics
    1. First
      1. Red to skin-colored firm, round Papule
      2. Rapid growth into dome-shaped Nodule
        1. May reach up to 1-2 cm in size within weeks to months
      3. Central umbilicated keratinous core
      4. Smooth surface
    2. Later (after 4-6 months)
      1. Lesion regresses over months
      2. Keratin core expelled
      3. Hypopigmented scar remains
  2. Distribution (sun-exposed areas)
    1. Face
    2. Extremities

VI. Differential Diagnosis

  1. Squamous Cell Skin Cancer
    1. Similar grossly and histologically to Keratoacanthoma

VII. Labs: Biopsy

  1. Biopsy lesions suspicious for Squamous Cell Skin Cancer (especially larger lesions)
    1. Exam and pathology findings can not always reliably distinguish keratocanthoma from SCC
    2. Complete excision with 3-5 mm margins is preferred overall
    3. Punch Biopsy is preferred over Shave Biopsy (depth may be inadequate otherwise)

VIII. Management

  1. Small Keratoacanthoma
    1. Electrodessication and Curettage
    2. Blunt Dissection
  2. Larger Keratoacanthoma
    1. Excision with 3-5 mm margins
    2. Moh's Surgery for difficult areas (esp. in regions with cosmetic concerns)
  3. Other options (non-surgical candidates, multiple lesions, inoperable skin sites)
    1. Topical agents
      1. 5-Fluorouracil 5% cream
        1. Apply during rapid growth tid
        2. Use under tape Occlusion
        3. Effective in 1-6 weeks
      2. Podophyllum 25% in benzoin
        1. Remove central crust and apply every 2 weeks prn
        2. Apply in clinic only due to high concentration
    2. Intralesional injections during rapid growth phase
      1. 5-Fluorouracil intralesional injection
      2. Methotrexate intralesional injection
      3. 5-Interferon alfa-2a injection
    3. Oral agents (for multiple lesions)
      1. Isotretinoin (Accutane)
    4. Radiotherapy
      1. Indicated for difficult cosmetic areas

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