What Is Acral Lentiginous Melanoma?
Acral melanoma is a skin condition that arises on the soles or palms and is a type of melanoma. The main feature of this condition is the location of the disease, such as the sole, palm, or beneath the nail. If it arises beneath the nail, it is called subungual melanoma. It is more common on feet than on hands. It can appear spontaneously or from a previously existing nevus or mole. Melanin pigments are responsible for skin discoloration; these pigments are produced by melanocytes. Melanoma is cancer affecting melanocytes.
Acral lentiginous melanoma begins as a flat patch of discolored skin; the malignant cells are first localized and remain within the area of origin, which can remain like that for months or even years. Acral lentiginous melanoma can then become invasive and cross the basement membrane; thereby, the cancerous cells can enter the dermis. In some cases, the lesion can be rapidly growing and penetrate deeper into the skin.
What Are the Causes of Acral Lentiginous Melanoma?
The exact cause of the condition is unknown; sun exposure has been ruled out as a potential cause. The disease evolves due to the malignant changes in the melanocytes (melanin pigment-producing cells). This malignant transformation can occur in a previously existing melanocytic nevus or can arise in normal skin. But what is, the triggering factors for this cancerous transformation are not entirely understood.
What Are the Clinical Features of Acral Lentiginous Melanoma?
Acral lentiginous melanoma is seen on the palm, soles, fingers, or toes. It appears as a discoloration that slowly enlarges. It can also appear without any pigmentation (amelanotic) or appear red.
The ABCDE rule is applied to this lesion, the same as that of other melanomas. Asymmetry, border irregularity, color change, large diameter or size, and evolving.
Other characteristic features include:
Size: large size, more than six millimeters or more.
Ulceration or bleeding may be present.
At first, the surface may be smooth, which slowly changes into an irregular surface.
The pigmentation varies; it can be brown, red, blue-gray, or black.
Acral melanoma arising in the nail region is called melanoma of the nail unit. If it begins in the nail growth area or matrix, it is known as subungual melanoma. It can appear as a diffuse discoloration or longitudinal bands which are pigmented and irregular. In advanced melanoma, the nail plate is completely destroyed.
Melanoma is a relatively serious form of skin cancer involving melanocytes.
Incidence: Acral lentiginous melanoma constitutes about one to three percent of melanomas in populations such as Australia and New Zealand. It is relatively rare in comparison to other forms of melanoma.
Racial Predilection: There is no correlation between skin color and this form of melanoma. It can occur at equal rates in white, black, or brown skin.
Gender Predilection: It can occur equally in men and women.
Age: It is more common in people over the age of 40.
How to Diagnose Acral Lentiginous Melanoma?
This test uses dermatoscope. It is useful in identifying acral lentiginous melanoma from other lesions such as moles (melanocytic nevi), viral warts, or bleeding. Acral lentiginous melanoma has dermoscopic features such as asymmetrical color and structure, blue-gray structure, and parallel ridge pattern of distribution.
A biopsy is a frequently used diagnostic tool to identify or confirm skin lesions or cancers. An excisional biopsy is done if acral lentiginous melanoma is suspected. A partial biopsy is avoided unless the lesion is extensive. Incisional biopsy is also avoided unless there is a large lesion and surgery cannot be done before a confirmatory diagnosis. In such cases, and in large lesions, several biopsies are performed at different sites so as to not miss out on a malignant focus.
Staging a cancerous lesion is finding how much the disease has spread from the original site of the skin.
Stage 0 — In situ melanoma.
Stage 1 — Melanoma less than 2 mm in thickness.
Stage 2 — Melanoma larger than 2 mm in thickness.
Stage 3 — Melanoma spreads to involve local lymph nodes.
Stage 4 — Distant metastases have been detected.
How Is Acral Lentiginous Melanoma Treated?
Being a cancerous condition, the ideal treatment is to surgically remove the lesion.
The lesion is excised with two to three millimeters of healthy tissue; this is done so as to make sure no remnant of the lesion is left behind.
A flap or graft may be required in certain cases to close the wound. In subungual melanoma, digits may be amputated partially in some cases. If the pathologist reports incomplete removal of melanoma, further surgery or radiation therapy may be required to ensure the complete removal of the tumor.
Melanoma in the site of origin — excision margin five millimeters.
Melanoma size: < 1.0 mm — excision margin one centimeter.
Melanoma size: 1.0–2.0 mm — excision margin one to two centimeters.
Melanoma size: 2.0–4.0 mm — excision margin one to two centimeters.
Melanoma size: > 4.0 mm — excision margin two centimeters.
What Is the Prognosis of Acral Lentiginous Melanoma?
Acral melanoma is not dangerous if it is restricted to the site of origin; however, if it becomes invasive, it can become life-threatening. The spread of melanoma depends on several factors. The most important is the size of the melanoma surgically removed. The chances for metastasis are rare if the size is less than 0.75mm. The chance is five percent if the thickness is between 0.75 to 1 mm, with the risk increasing with size. A size greater than four millimeters has a 50 % survival rate after ten years.
Acral lentiginous melanoma is a rare form of melanoma, with its characteristic feature being the site of origin being palms, soles, or nails. It begins as a discoloration on the skin, which can progress and become invasive. The treatment is based on the stage of melanoma and the size of the excised lesion. Surgery is the first line of treatment; the follow-up therapy depends on the extent of metastasis.