Lentigo maligna melanoma

Overview

Lentigo maligna melanoma is a melanoma that has evolved from a lentigo maligna. They are usually found on chronically sun damaged skin such as the face and the forearms of the elderly. The nomeclature is very confusing to both patients, dermatologists, and pathologists alike. Lentigo maligna is the non-invasive skin growth that some pathologists consider to be a melanoma-in-situ. A few pathologists do not consider lentigo maligna to be a melanoma at all, but a precursor to melanomas. Once a lentigo maligna becomes a lentigo maligna melanoma, it is treated as if it were an invasive melanoma.

Causes

Lentigo maligna is a proliferation of malignant pigment cells (melanocytes) along the basal layer of the epidermis and within the hair follicle. What triggers the cells to become malignant is unknown but genetic mutations may start within primitive stem cells.

Sun exposure:

  • Sun exposure has long been suspected to be a risk factor; however, a meta-analysis of melanoma case-control studies found:
      • Low relative risks associated with various measures of exposure to UV radiation and the relation with sunshine was not dose-dependent.
      • Sharp, short bursts of acute exposure in childhood, and severe sunburn, were most strongly associated with melanoma.
      • Occupation and leisure, eg airline crew, gardeners, cricketers and those involved in other outdoor pursuits. However, cumulative moderate occupational exposure seems to be protective in some white populations.
  • Host response to UV radiation appears to be more important than dose of sun exposure.
  • Past sunbed use, especially before age 30

Diagnosis

  • Most melanomas that are detected and treated early are cured.
  • In the UK as a whole, the overall 5-year survival rate is 73% in men and 85% in women.
  • Survival among melanoma patients decreases with increasing age and is lower among males.The melanoma mortality rate has increased over the last 25 years for men but not women.
  • Survival in melanoma is strongly correlated with the depth of invasion at diagnosis (Breslow thickness).
  • The risk of death from a primary melanoma increases dramatically with increasing stage. Patients with metastatic disease have a median survival of six to nine months.
  • Women have thinner tumours and survive melanoma better than men even after adjustment for Breslow thickness, ulceration and body site.
  • 8% of all melanoma patients develop a second melanoma within 2 years of their initial diagnosis. Melanoma patients also have increased risks for other skin tumours. In patients with lentigo maligna melanomas, 35% of the patients developed another cutaneous malignancy within 5 years.
  • Patients with in-transit metastases (deposits from a focus of cells moving along regional lymphatic channels) have a poor prognosis, with a 5-year survival rate of only 25%. In-transit metastases and nodal metastases are generally treated surgically with palliative intent.

Treatment

Is dependent on the thickness of the invasive component of the lentigo maligna. Treatment is essentially identical to other melanomas of the same thickness and stage.