Msk Dermatology · Year 2 · from Msk Dermatology

Case 4: Actinic Keratosis with Field Cancerization

Patient Presentation

Demographics: 72-year-old male

Chief Complaint: Multiple rough patches on scalp and face

History of Present Illness: The patient has noticed multiple rough, scaly patches on his bald scalp and face over the past several years. Some have been treated with cryotherapy in the past, but new ones keep appearing. He spent most of his career working outdoors as a farmer.

Past Medical History:

  • Multiple actinic keratoses (previously treated)
  • One SCC on ear (excised 3 years ago)
  • Fitzpatrick type II skin

Physical Examination:

  • Scalp:
  • Multiple (>15) erythematous, scaly papules and patches
  • 3-8 mm in size
  • Rough, sandpaper-like texture
  • Surrounding photodamaged skin with telangiectasias
  • Face:
  • Multiple AKs on forehead and temples
  • Solar elastosis
  • One lesion on right temple appears more indurated and thickened

Workup and Results

Clinical Assessment:

  • Field cancerization: Multiple AKs in sun-damaged skin
  • One suspicious lesion (right temple) biopsied

Biopsy (right temple lesion):

  • Squamous cell carcinoma in situ (Bowen disease)

Clinical Image

Clinical photograph showing multiple actinic keratoses on the bald scalp with characteristic rough, scaly appearance and surrounding photodamaged skin, demonstrating field cancerization.

Diagnosis

Field Cancerization with Multiple Actinic Keratoses and SCC in Situ (Bowen Disease)

Features:

  • Multiple AKs in sun-damaged field
  • One lesion progressed to SCC in situ
  • High-risk patient (history of SCC, ongoing sun damage)

Discussion

This case illustrates actinic keratoses and field cancerization:

  • Precursor Lesion: The lecture identifies actinic keratosis as a precursor lesion for SCC, with 1-10% progressing to invasive carcinoma.
  • Field Cancerization: The lecture describes field cancerization as multiple lesions in a sun-damaged area requiring field-directed therapy rather than individual lesion treatment.
  • Bowen Disease: The lecture identifies Bowen disease as squamous cell carcinoma in situ (full-thickness epidermal dysplasia without dermal invasion).
  • Field-Directed Therapies: The lecture lists field-directed options including topical 5-fluorouracil, imiquimod, and photodynamic therapy. Mohs surgery is lesion-specific, not field therapy.

Treatment Plan

  1. For SCC in Situ (Right Temple):
  • Excision with clear margins
  • OR Mohs surgery (cosmetically sensitive area)
  1. Field-Directed Therapy:
  • Topical 5-fluorouracil (5-FU) 5% cream
  • Apply twice daily for 2-4 weeks
  • Expect significant inflammation (therapeutic)
  • OR Imiquimod 5% cream (3x/week for 4-8 weeks)
  • OR Photodynamic therapy (PDT)
  1. Individual Lesion Treatment:
  • Cryotherapy for isolated thick lesions
  • Can be used in conjunction with field therapy
  1. Prevention:
  • Daily sunscreen SPF 30+
  • Wide-brimmed hat
  • Avoid midday sun
  1. Surveillance:
  • Skin exams every 3-6 months given history of SCC
  • Prompt evaluation of any changing or indurated lesions

Teaching Points

  1. Actinic keratosis is a precursor to SCC (1-10% progress)
  2. Field cancerization requires field-directed therapy (5-FU, imiquimod, PDT)
  3. Bowen disease = SCC in situ
  4. UVB causes pyrimidine dimers (DNA damage)
  5. Fitzpatrick type I-II at highest risk for skin cancer

Image Reference

For visual reference of skin cancer concepts, see:

Learning Points

  1. BCC Features: Pearly, translucent, arborizing vessels; Mohs achieves >99% cure
  1. SCC in Transplant: 65-fold increased risk; anti-PD-1 is first-line for advanced disease
  1. Melanoma Prognostic Factors: Breslow depth most important; SLNB for >0.8mm; BRAF in ~50%
  1. Actinic Keratosis: 1-10% progress to SCC; field cancerization requires field therapy
  1. Surgical Margins for Melanoma: In situ: 0.5-1cm; 1-2mm: 1-2cm; >2mm: 2cm

All cases for this lecture as Markdown