Last reviewed by Editorial Team on August 13th, 2018.
What is Acral Lentiginous Melanoma?
Acral lentiginous melanoma is a rare type of melanoma that involves the palms of the hands and the soles of the feet. This type of melanoma can also occur under the nail. It is fairly common among darker skinned individual and rare among Caucasians.
Acral lentiginous melanoma occurs more commonly in the soles of the feet rather than in the palms of the hands. During the in situ phase of the condition, the malignant cells linger inside the tissue of its origin, which can take several months to several years. It becomes insidious when the malignant cells gain entry into the dermis when melanoma cells reach the basement membrane of the outermost layer of the skin.
Melanoma is a more serious form of skin cancer as it has the capability to spread to other parts of the body distant from its origin, which poses a threat to the health and which can be fatal. It is a type of cancer that develops in the pigment cells of the skin or known as melanocytes. The visible site of development of melanoma makes it easier to recognize and which makes the patients themselves to first recognize the onset of melanoma. Melanoma occurs anywhere it the skin and is therefore classified according to the site of the development and characteristics. Acral lentiginous melanoma is among its type although this type is rather rare in frequency. It is a type of melanoma that commonly develops on the palms of the hands and soles of the feet and including the area beneath the nails.
Acral lentiginous melanoma equally affects both men and women and can affect people worldwide without racial predilection. It has, however, a slight prevalence among Asians and dark skinned individual and those of Asians. It usually occurs in people aged 40 years and above add is usually diagnosed around the age of 60 years to 70 years.
Recognition of melanoma including its variants is guided by the ABCD rule.
The ABCD rule stands for:
A – Asymmetry of the lesion that developed
B – Border of the lesion characterizing its irregularity
C – Color changes of the lesion which is far from the normal skin tone
D – Diameter describing the size of the lesion
Acral lentiginous melanoma initially starts as an enlarging patch of skin in the areas of the palms of the hands and soles of the feet including the fingers and the toes. The patches at first look like an ordinary pigmented macules and grow gradually. The size of the lesion gradually increases and which becomes more irregular in shape relative to the increase in size. The color of the lesion also changes as it slowly increases in size.
The lesion of acral lentiginous melanoma is rather flat and will remain flat even if it has reached the deeper layer of the skin. Thickening of the lesion makes walking difficult as it can be painful and is sometimes mistaken for a plantar wart.
The lesion of acral lentiginous melanoma is characterized by the following:
- The size of the lesion is approximately 6 mm in diameter and can be more than several centimeters in diameter usually when diagnosed
- There are various colors or pigmentation ranging from black, blue-gray, red and brown
- The surface of the lesion is usually smooth at first and later become dry
- The shape of the lesion is irregular and becomes more irregular as it increases in size
- The lesion may also have bleeding and ulceration
Acral lentiginous melanoma may also develop beneath the nail and is termed as subungual melanoma. The lesion usually develops in the thumb or in the big toe although it can appear in any fingers of the hands and toes of the feet and initially appears as a nail streak. The melanoma in subungual melanoma originates from the nail matrix.
Subungual melanoma is a variant of acral lentiginous melanoma and is characterized by the following:
- Formation of new nail streak that does not come from a recent injury or trauma
- Nail streak that gradually increases in size
- Nail streak that is becoming darkly pigmented
- Nail that is splitting from the nail bed
- Nail plate that has been obliterated is a sign of advance stage of acral lentiginous melanoma
Growth of lesion in the fingers, toes, palms of the hands and soles of the feet including the area beneath the nail should not be neglected and instead brought to a dermatologist for proper evaluation. There are certain cases where the lesion in acral lentiginous melanoma as the lesion may appear like chronic infection. It is also advisable to take notice of the changes that may occur in the lesion as not all lesions that appears on the palms of the hands and soles of the feet, including the area beneath the nail are tantamount to the onset of acral lentiginous melanoma. There are other skin conditions which have similar presentation with acral lentiginous melanoma that evaluation from a doctor is necessary to isolate acral lentiginous melanoma and to seek prompt treatment when necessary.
Acral lentiginous melanoma occurs as a result of malignant melanocytes occurring at the basement membrane of the outer layer of the skin. The exact cause of growth of malignant melanocytes is not clearly understood. Genetic mutation, however, is being linked to the incidence of acral lentiginous melanoma.
The initial action in treating acral lentiginous melanoma is to completely excise the lesion with a margin of 2 to 3mm from the normal tissue. The treatment plan will also depend on the thickness of the lesion as described by the Breslow thickness and the level of invasion as described by Clark level.
Breslow thickness and Clark level of invasion are both used in the diagnosis of acral lentiginous melanoma in determining how far the acral lentiginous melanoma has reached and in staging the melanoma.
Partial amputation of the affected digit may be necessary in the case of acral lentiginous melanoma particularly in the case of subungual melanoma. Further treatment and therapy is recommended after evaluation of the excised melanoma and after proper staging has been established.
The prognosis for acral lentiginous melanoma in situ is often good and not dangerous. The danger occurs when melanoma has invaded the basement membrane of the outer layer of the skin that has gained entry into the dermis later allowing spread of the malignant melanocytes. The invasion of malignant melanocytes and the degree of its spread will determine the seriousness of the disease which is potentially life-threatening. The main factor in determining the risk of metastases is the measurement of the thickness gained at the time of the surgical removal of the melanoma.