Pathology in Cutaneous Melanoma

An experienced dermatopathologist is an important member of the multidisciplinary melanoma team:
- That contributes to the accurate diagnosis and staging of patients with melanoma
It is my practice to have outside biopsies reviewed by our pathology staff upon referral to confirm diagnosis
Although the pathologic analysis primarily consists of microscopic examination of hematoxylin- and eosin-stained tumor:
- Several melanocytic cell markers may also be useful to confirm the diagnosis
- Two antibodies that have been widely used in immunohistochemical evaluations are:
  - S-100 and HMB-45:
    - S-100 is expressed not only by more than 90% of melanomas:
      - But also by several other tumors and some normal tissues, including dendritic cells
    - In contrast, the monoclonal antibody HMB-45:
      - Is relatively specific (yet not as sensitive) for proliferative melanocytic cells and melanoma
      - It is therefore often used as a confirmatory stain when the diagnosis of melanoma is being considered
  - Anti–MART-1 staining has also been shown to be very useful in the diagnosis of melanoma
  - The major histomorphologic components that should be included in a primary melanoma pathology report include:
    - Breslow thickness
    - Ulceration status
    - Peripheral and deep margin status
    - Mitotic rate:
      - Using the dermal hot spot approach with units of mitoses per mm²
    - Other features that are often also recorded include:
      - Presence of microsatellites
      - Histologic subtype
      - Lymphovascular invasion
      - Tumor-infiltrating lymphocytes (TIL)
      - Regression
      - Neurotropism
      - Growth phase
      - The absence of epidermal component:
        As the latter may represent an uncommon dermal primary or a metastatic deposit
The major histomorphologic types of melanoma:
- Superficial spreading melanomas:
  - Constitute the majority of melanomas:
    - Approximately 70% of melanomas
  - Generally arise in a pre-existing nevus
Nodular melanomas:
- Are the second most common type:
  - 15% to 30% of melanoma
- Nodular melanomas progress to invasiveness more quickly than other types:
  - However, when depth of the melanoma is controlled for:
    - Nodular melanomas are generally associated with the same prognosis as other lesions
Lentigo maligna melanomas:
- Constitute a small percentage of melanomas:
  - 4% to 10%
- These lesions occur in sun-exposed areas
- Lentigo maligna melanomas are classically located on:
  - The faces of older white women
- In general, lentigo maligna melanomas are:
  - Large (> 3 cm at diagnosis)
  - Flat lesions
  - Are uncommon in individuals younger than 50 years
- Given their often-ill-defined appearance:
  - Margin control can sometimes be challenging at the time of wide excision
Acral lentiginous melanomas:
- Occur on the palms (palmar), soles (plantar), or beneath the nail beds (subungual):
  - Although not all palmar, plantar, and subungual melanomas are acral lentiginous melanomas
- These melanomas account for only 2% to 8% of melanomas in white patients but for a substantially higher proportion of melanomas (35% to 60%) in darker-skinned patients
- They are often large:
  - With an average diameter of approximately 3 cm
Amelanotic melanomas:
- Are relatively uncommon melanomas that occur without pigmentation changes
- They are often more difficult to diagnose because of their lack of pigmentation
- Factors such as:
  - Change in size
  - Asymmetry
  - Irregular borders may suggest malignancy and prompt a biopsy, but delays in diagnosis may sometimes be observed
While melanoma has been traditionally described using these categories:
- Prognosis is more dependent upon staging than by these histomorphologic types