lentigo maligna melanoma
Monday 21 February 2005
lentigo maligna; Dubreuilh melanosis
UI:1832 - melanoma in situ (lentigo maligna)
Lentigo maligna melanoma occurs most frequently on the face and sun-exposed upper extremities of elderly people.
Its precursor lesion, the lentigo maligna (Hutchinson’s melanotic freckle), is an irregularly pigmented macule which expands slowly.
It should be noted that the recent WHO publication on tumors of the skin has stated that ‘lentigo maligna (LM) is a form of melanoma in situ …’, which means it is not a precursor but the same entity.
There is great variation in color, with tan-brown, black, and even pink areas present. Perioral lesions rarely spread onto oral mucosa.
An amelanotic variant has been reported; rarely, this takes the form of an inflammatory plaque or follows cryosurgery or other therapy for lentigo maligna.
Invasive malignancy (vertical growth phase) is characterized by thickening of the lesion with the development of elevated plaques or discrete nodules.
The proportion of lentigo malignas that progress to lentigo maligna melanoma is said to be quite small, with a lifetime risk of only about 5%.
Rapid progression to a deeply invasive tumor has been reported.
A contiguous solar lentigo is present in 30% of lentigo malignas and a pigmented actinic keratosis in 24%.
The latter lesion is frequently confused with melanoma on dermoscopy.
A significant number of lentigo malignas arise in a patch of solar lentigo of long duration.
In other parts of the solar lentigo, evolution into a seborrheic keratosis may also occur.
Cryotherapy, topical imiquimod, imiquimod with cryotherapy, radiotherapy, surgical excision with mapping or peripheral vertical ± horizontal sections for margin control, and a modified Mohs micrographic technique, using immunoperoxidase staining with HMB-45, or MART-1, have all been proposed as suitable methods of treatment for lentigo maligna.
Dermoscopy and confocal microscopy have been used to better define the edge of a lentigo maligna prior to surgery. Staged excision can also be used.
In a recent study, staged excision was associated with a significantly lower recurrence rate compared to Mohs surgery.
Clinical margins of 5 mm or 6 mm result in inadequate excisions in approximately 15% of patients.
Unfortunately, cryotherapy may be followed by lentiginous hyperpigmentation in the scar, which requires differentiation from a recurrence.
Topical 1% cidofovir was used successfully in two cases involving the cheek in elderly patients.
The use of treatment modalities other than surgical excision for melanoma in situ carries a significantly increased risk of local recurrence. There is no consensus, at least in the United States, as to what surgical margins should be in cases of melanoma in situ.
10q26 rearrangements (#1606557#)
Grammatico P, Modesti A, Steindl K, Scarpa S, Heouaine A, Picardo M, Del Porto G. Lentigo maligna. Cytogenetic, ultrastructural, and phenotypic characterization of a primary cell culture. Cancer Genet Cytogenet. 1992 Jun;60(2):141-6. PMID: #1606557#