acral lentiginous melanoma

Introduction

Cutaneous melanoma arising on the sole, palm, fingernail or toenail bed, or mucocutaneous skin of the mouth, genitalia or anus.

Epidemiology

• occurs most often in Asians, sub-Saharan Africans & African Americans (50-70% of melanomas in these populations)
• 7-9% of all melanomas, 2-8% in whites
  • most common skin cancer in people of skin color
• median age: 60-65 years
• male:female ratio is 3:1
• only melanoma subtype not associated with sun exposure

Pathology

• intense lymphocytic infiltration at the dermal-epidermal junction
• large melanocytes with prominent dendrites along the basal cell layer
• melanocytes may form large nest extending into the dermis & along eccrine ducts
• invasive malignant melanocytes often have a spindle shape giving the tumor a desmoplastic appearance

Clinical manifestations

• slow growing tumor (2.5 year from appearance to diagnosis)
• palm or sole (volar) type
  • macular lesion in the radial growth phase with focal papules & nodules developing during the vertical growth phase
  • color: marked variegation, blue, brown, black & depigmented pale areas
  • 3-12 mm in size
  • irregular borders, may be sharply or ill-defined
  • distribution: soles, palms, fingers & toes
• subungual type
  • subungual macule beginning at the nail matrix, extending to involve the nail bed & nail plate
  • papules, nodules & destruction of the nail plate may occur in the vertical growth phase
  • color: dark brown to black pigmentation that may involve entire nail, often nodules & papules are unpigmented, may be amelanotic
  • distribution: thumb or great toe
  • periungual pigmentation (Hutchinson's sign)
• mucous membrane

* images

Differential diagnosis

• plantar wart
• subungual hematoma; subungual hemorrhage
  • pigmentation progresses distally as nail grows out creating a zone of clearing between the proximal nail fold & the pigmentation
• fungal infection
• pyoderma gangrenosum

Management

• prognosis
  • 5 year survival for volar type is 50%
  • 5 year survival of subungual type is 80%
• examine regional lymph nodes
• surgical excisions
  • melanoma in situ
    • excise with > 5mm margin
  • thickness < 1 mm
    • excise with 10 mm margin
    • excise down to fascia or muscle if no underlying fascia
    • direct closure without graft often possible
    • node dissection only if palpable & suspscious for metastasis
  • thickness 1-4 mm
    • excision with 20 mm margin
    • excise down to fascia or muscle if no underlying fasica
    • regional lymphadenectomy if sentinel node procedure is positive
    • lymph node dissection if regional lymph nodes are palpable
  • thickness > 4 mm
    • excision with 30 mm margin
    • excise down to fascia or muscle if no underlying fascia
    • lymph node dissection if regional lymph nodes are palpable
      • • amputation may be indicated
• adjuvant chemotherapy
  • interferon alpha-2b
  • melphalan

More general terms

• cutaneous melanoma