Acral lentiginous melanoma (ALM) is a form of skin cancer that appears on the palms of the hands, the soles of the feet, or under the nails.
ALM accounts for 2–3% of all melanomas.
In this article, we look at the symptoms of ALM, how doctors diagnose and stage it, and the treatment options.
Most melanomas result from exposure to ultraviolet (UV) radiation from the sun. They occur most often in people with light skin, which is more prone to damage from UV radiation.
ALM, however, does not appear to stem from sun exposure. It can affect people with any skin color, but it is the leading cause of melanoma in people with darker skin.
ALM is a type of melanoma that develops on the palms, soles, and the skin under the nails.
ALM sometimes develops from an existing mole, but it can also occur for no apparent reason on healthy skin.
Find out more about how skin cancer affects black people.
An early sign might be an oddly shaped black, gray, tan, or brown mark with irregular borders.
When ALM begins in the nails, it may appear as a streak under the nail. Most cases of ALM on the nails occur on the big toe or thumb.
Other warning signs include:
- a new streak in a nail that is not due to 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
- a raised, thickened patch on the sole or palm
- pain when walking
Here are some other points to be aware of:
- The surface may be flat, but there may be deep inward growth.
- Some tumors involve a loss of color or no change in color.
- ALM tumors often take on an irregular shape or color or a rough texture as they grow.
- ALM may resemble a plantar wart or a fungal infection.
Anyone that suspects they may have cancer on the soles of their feet should see a doctor or dermatologist.
What are the symptoms of skin cancer? Learn more here.
Anyone can develop ALM.
Some people may develop ALM due to a genetic risk factor. People whose family members have developed melanoma, including ALM, may be more prone to the disorder.
Research into the specific causes and risk factors for ALM is ongoing.
Some experts have suggested that an ALM lesion may follow an injury to the hand or foot. Authors of a small 2016 study proposed that inflammation may play a role. However, there is not enough evidence to confirm a link.
However, most people with ALM do not have an injury, and most people who injure their hands or feet never develop ALM.
ALM can affect the soles, the palms, or the nails. It most commonly appears on the soles of the feet.
The doctor will ask the person about their symptoms and examine the affected area. ALM and other forms of cancer have a particular appearance that will help a doctor decide which tests are appropriate.
If symptoms suggest that cancer might be present, the next step is usually a biopsy. A doctor will use a needle to collect a sample of skin cells for examination under a microscope. A biopsy can show if cancer is present and, if so, what type.
The doctor will look at the person's palms, soles, and nailbeds.
They may look for lesions that:
- measure from 6 millimeters (mm) up to several centimeters (cm) across
- are a mixture of brown, blue-grey, black, and red
- have a smooth surface in the early stages, becoming thicker with time
- have an irregular and possibly dry or warty surface
- show signs of ulceration or bleeding
What other types of melanoma can affect the feet? Click here to learn more.
The stage of a cancer describes how far it has spread. Knowing the stage can help doctors establish a treatment plan. It can also give them an idea about an individual's outlook.
The American Joint Committee on Cancer (AJCC) stage melanoma according to three main factors:
- Lymph nodes
This is known as the TNM system. The doctor gives points to each factor. Tumors develop in different ways, so assessing the size of a lesion alone may not provide an accurate picture. Combining these three factors can give the doctor an idea of the stage the cancer has reached.
For ALM, the doctor will look at:
Tumor: Numbers range from 0–4, depending on a variety of factors, including the size of the tumor and whether there is ulceration. Lower numbers indicate a smaller tumor.
Nodes: The scale ranges from 0–3, depending on the extent to which cancer has affected the lymph nodes.
Metastasis: This refers to the spread of cancer from one area of the body to another. When cancer metastasizes, it is usually an indication that it is in the late stage. It is also harder to treat and more likely to be fatal. Metastasis scores range from 0–1. A score of 1 indicates some metastasis, with letters a, b, and c indicating progressively more spreading.
Doctors may also assign a Clark level, which describes how far cancer has invaded the body.
Clark levels range from 1–5, with higher numbers reflecting more invasive cancers.
Find out more about late-stage melanoma.
Treatment usually begins with removing the lesion and some of the healthy surrounding skin. If cancer affects any lymph nodes, the surgeon may remove these, too.
In some people, this treats the cancer. But if the cancer has progressed or is very aggressive, they may need other treatments.
A doctor may also recommend medication to prevent any remaining cancer cells from spreading.
A doctor will give this drug by intravenous infusion. Chemotherapy aims to destroy cancer cells, but it can also destroy healthy cells and may result in severe adverse effects.
People should speak to their doctor about their treatment plan, what to expect, and what to do if adverse effects occur.
Some people may be able to take part in clinical trials, which can offer access to new treatments that are not yet widely available.
Experts do not yet know what causes ALM, and they also do not know how to prevent it.
The best way to prevent ALM from becoming severe is to get an early diagnosis.
Ways of doing this include:
- seeking an annual skin exam to test for skin cancer
- seeking medical help if an unexplained lesion appears on a hand, foot, or nail
People who have a close relative with ALM should monitor for skin changes and see a doctor if any unusual lesions develop.
Death rates from ALM are higher than those of other forms of melanoma. This may be because people often do not notice or recognize ALM until a later stage when it has already started to progress and become more aggressive.
Early diagnosis and prompt treatment affect the outlook and life expectancy for ALM. However, doctors often misdiagnose ALM. This may be because it is relatively uncommon or because it can resemble other, less serious, health issues.
Overall, the outlook for thinner and early stage tumors is better. Raised tumors tend to be more aggressive.
A 2009 report notes that aggression and outlook with ALM tend to vary not only across stages but also in different population groups. This 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.
Survival rates also vary. The report found that:
Non-Hispanic white people have an average 82.6% chance of surviving at least another 5 years after a diagnosis of ALM, and 69.4% survive 10 years or more.
African American people have an average 5-year survival rate of 77.2% and 71.5% for 10 years or more.
Hispanic people have a 5-year survival rate of 72.8%, with 57.3% surviving 10 years or more.
Asian people and Pacific Islanders have a 5-year survival rate of 70.2%, with 54.1% surviving to 10 years.
The authors say that people in the groups that have lower survival rates tend to have thicker tumors and a more advanced stage of cancer at diagnosis.
ALM is rare, but it can be life-threatening. People have a better chance of spotting ALM and getting help if they monitor their skin for changes and seek medical help if lesions develop.
With early diagnosis, many people have a good chance of effective treatment.