http://www.histopathology-india.MelanocyticTumours.htm

Lentigo maligna melanoma most  frequently  occurs on the sun-exposed  face and upper extremities of elderly people.

Lentigo maligna is the precursor lesion and is characterized by an irregular pigmented macule which expands slowly . The invasive malignant tumour grossly presents as a raised plaque or a discrete nodule.

Histologically, there is proliferation of atypical melanocytes singly and  in  nests along the basal layer of the epidermis. The atypical cells are small with prominent nucleoli and characteristic pericellular halo due to fixation artifact. Multinucleate cells with dendritic processes are often present. The melanocytes grow along the upper portion of hair follicle and extends to the level of sebaceous gland duct.  There is often epidermal atrophy.

The dermal component may be composed of spindle or epithelioid cells. In some cases, numerous mitotic figures may be present. The superficial dermis often shows  prominent solar elastosis together with  scattered  pigment containing macrophages. Patchy inflammation and fibrosis may be noted in the upper dermis associated with invasion into superficial dermis.

Lentigo maligna and lentigo maligna melanoma  may clinically resemble other pigmented lesions such as solar lentigo or a superficial malignant melanoma.  Rarely, amelanotic lentigo maligna may resemble dermatitis or Bowen's disease.

Histologically, it may be difficult to outline the lateral borders of the lesion as the scar damaged skin may have an increased number of melanocytes and may have occasional atypical melanocytes in the basal layer. Often actinic keratosis and lentigo maligna co-exist. Atypical keratinocytes in actinic keratosis may cause further problem in making  histological diagnosis.

It may be difficult to identify  the microinvasive foci even after multiple levels. Spindled melanocytes may resemble fibrohistiocytic cells and be obscured by inflammatory cells and heavily  pigmented melanophages. These cells may be highlighted by S100 protein and HMB45 immunostains.

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Lentigo maligna/lentigo maligna melanoma: current state of diagnosis and treatment.Dermatol Surg. 2006 Apr;32(4):493-504.

A collision tumor involving Basal cell carcinoma and lentigo maligna melanoma.Am J Dermatopathol. 2005 Aug;27(4):319-21.

Lentiginous melanoma: a histologic pattern of melanoma to be distinguished from lentiginous nevus.Mod Pathol. 2005 Oct;18(10):1397-401.

Progression to invasive melanoma from malignant melanoma in situ, lentigo maligna type.Hum Pathol. 2000 Jun;31(6):705-8.

Lentigo maligna and malignant melanoma in situ, lentigo maligna type.Hum Pathol. 1999 May;30(5):533-6.

Prognostic parameters of melanoma

Lentigo maligna melanoma

Superficial spreading melanoma

Nodular melanoma

Acral lentiginous melanoma

Desmoplastic /Spindle cell /
Neurotropic melanoma

Naevoid melanoma

Balloon cell melanoma