Acral Lentiginous Melanoma (ALM)

What is acral lentiginous melanoma?

Acral lentiginous melanoma (ALM) is a specific type of melanoma that appears on the palms of the hands, the soles of the feet, or under the nails. Melanocytes contain your skin color (known as melanin or pigment). In this type of melanoma, the word “acral” refers to the occurrence of the melanoma on the palms or soles. The word “lentiginous” means that the spot of melanoma is much darker than the surrounding skin. It also has a sharp border between the dark skin and the lighter skin around it. This contrast in color is one of the most noticeable symptoms of this type of melanoma.

Though relatively uncommon in the general population, ALM is the most common type of melanoma in people with darker skin and those of Asian descent. However, it can be seen in all skin types. ALM may be hard to recognize at first when the patch of darkened skin is small and looks like little more than a stain or bruise.  ALM sometimes develops from an existing mole. It can also occur seemingly out of nowhere on healthy skin. Early diagnosis and treatment are essential.

Where ALM Can Develop

The most visible symptom of ALM is typically a dark spot of skin that’s surrounded by skin that remains your normal skin color. There’s a clear border between the dark skin and the lighter skin around it. You’ll usually find a spot like this on or around your hands and feet, or in the nail beds.

ALM spots may not always be dark-colored or even dark at all. Some spots may be reddish or orange in color — these are called amelanotic (or non-pigmented).

Warning signs of ALM include:

  • a new streak in a nail that is not caused by an accident or bruise
  • a nail streak that has damaged the fingernail
  • a changing spot in or connected to a mole on the foot or hand
  • an irregularly-shaped growth on the foot or hand that is changing, growing or has an unusual color
  • an elevated, thickened patch growing on the sole of the foot or palm of the hand

Palm or Sole

Most people first notice an oddly shaped black, gray, tan, or brown mark with irregular borders.

Acral lentiginous melanoma affects the feet and hands, as well as the skin beneath the nails. Image credit: Image credit: Will Blake, (2006, May 29)

Under a Nail

The first sign may be a “nail streak,” a narrow, dark stripe under the nail. ALM usually develops on the thumb or big toe; however, it can occur under any fingernail or toenail. Not all nail streaks are melanoma; many dark-skinned people may have nail streaks that are completely benign.  Most cases of ALM on the nails occur on the big toe or thumb. As the spot of ALM grows, your nail might begin to crack or break altogether, especially as it advances to later stages.

Subungual (nailbed) melanoma is less common but represents about 33% of melanomas in dark-skinned people. Characteristics include a brown or black linear nail band(s) often wider than 5 mm with a blurred or irregular border with the thumb and big toe being the primary nail site. Approximately half of these tumors may have little or no color leading to a delay in diagnosis. The colored nail band variety can be confused with a fungal infection (especially in the toe) or trauma thus leading to misdiagnosis and/or delay in treatment.

Causes and risk factors

Anyone can develop ALM. Unlike other forms of melanoma, ALM does not appear to be related to sun exposure. In some people, it may be due to a genetic risk factor. People whose family members have developed melanoma, including ALM, may be more prone to the disorder.

Death rates from ALM are higher than those of other forms of melanoma.  This may be because ALM goes unnoticed longer, allowing it to progress and become more aggressive before treatment begins. Early diagnosis and prompt treatment have a major impact on whether a person will survive. However, a large number of people who have ALM are initially misdiagnosed with something else.

Researchers do not know why survival and cancer aggression seems to vary across different groups. It could be due to differences in medical care or because some groups are more likely to notice and seek treatment for signs of skin cancer.

Prevention

Though ALM is rare, it can be deadly. Monitoring the skin for changes can be life-saving. As researchers do not yet know what causes ALM, they also do not know how to prevent it. The best opportunity for a favorable outcome is a prompt diagnosis. It is important to schedule an annual skin examination with your dermatologist. You should promptly see a doctor if an unexplained lesion appears on a hand, foot, or nail.  If you begin to see signs of ALM by using the ABCDE rule, see your doctor as soon as possible so that they can take a biopsy of the area and decide whether the spot is cancerous. As with any form of cancer or melanoma, diagnosing it early can help make treatment easier and the effect on your health minimal.

Other Things to Know About Acral Lentiginous Melanoma

As an ALM tumor increases in size, it usually becomes more irregular in shape and color (although some ALM lesions can be lightly colored or colorless).

The surface of the ALM lesion may remain flat, even as the tumor invades deeply into the skin.

Thickening ALM on the sole of the foot can make walking painful and be mistaken for a plantar wart.

The surface of a spot of ALM may also start out smooth and become bumpier or rougher as it evolves. If a tumor begins to grow from the cancerous skin cells, the skin will become more bulbous, discolored, and rough to the touch.

Less advanced cancers and thinner tumors have better survival rates. Raised tumors tend to be more aggressive.

Men are more likely than women to have thick, large tumors at diagnosis. A person’s race is also a factor, with non-Hispanic whites having lower rates of similar tumors at the time of diagnosis.

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