Acral lentiginous melanoma: 8 questions about this rare skin cancer

Many skin cancers — including cutaneous melanoma — are associated with UV exposure. Yet acral lentiginous melanoma develops only on areas of the body that can’t really be protected by sunscreen — and there’s no direct link to UV exposure.

So, what causes acral lentiginous melanoma? And how is it normally diagnosed and treated? To learn more about this rare skin cancer, we spoke with dermatologist Kelly Nelson, M.D., and melanoma specialist Isabella Glitza Oliva, M.D., Ph.D.

What is acral lentiginous melanoma?

Nelson: It’s a type of skin cancer that only develops on the palms of the hands, the soles of the feet or under the nails.

Glitza: It’s also very rare. Acral lentiginous melanoma only makes up about 5% of all new melanomas diagnosed each year.

What does acral lentiginous melanoma look like?

Nelson: Usually, acral lentiginous melanoma can appear as an unevenly pigmented black or brown spot on the palm or sole that looks different from the rest of the patient’s skin and grows over time. When acral lentiginous melanoma involves the nail, it may appear as a pigmented band or a streak of color growing from the cuticle out to the tip of the fingernail or toenail.  

How is acral lentiginous melanoma usually diagnosed?

Nelson: Sometimes it’s found during an annual physical, when a doctor checks someone’s toes for loss of sensation due to diabetes. Podiatrists are also trained to recognize it. 

Occasionally, people might notice something isn’t right and see a doctor. But they tend to be more aware of their hands than their feet. So, if something is on their hands, they usually have a better chance of finding it. Most people don’t regularly look at the bottom of their feet or in between their toes!

A dermatologist might also find acral lentiginous melanoma during a head-to-toe skin check, or while treating someone for another skin condition.

Is acral lentiginous melanoma more difficult to diagnose in people with darker complexions?

Nelson: Yes. But people with darker skin face a lot of challenges in their quest to get high-quality skin cancer care. One reason is that many people with light-complected skin know someone who’s had skin cancer, so they may already be aware of skin cancer or already seeing a dermatologist themselves. 

Skin cancer is also rarer in people with darker skin, so people with darker skin may be less likely to know another dark-skinned person who’s had skin cancer. And because of that, they may not ever think to look closely at their nail beds or examine the palms of their hands or the bottoms of their feet. Even if they do see something, they may not realize it’s skin cancer, because they don’t think it can happen to them. 

Often, people with acral lentiginous melanoma don’t come see us until something starts bleeding or it becomes uncomfortable when they walk. And I can’t tell you the number of times I’ve heard patients say, “I thought it was just a bruise,” or a blood blister or a wart. 

Glitza: Another reason acral lentiginous melanoma is harder to diagnose is because it doesn’t appear in the same way that other types of skin cancer and melanoma do. While we normally look for changes in symmetry, border and other areas for most skin cancers, that doesn’t work for this type of melanoma. The “ABCDE” guide for melanoma doesn’t really apply here, so we have to use a different memory prompt. The one we use for acral lentiginous melanoma is called "CUBED," which stands for "Color, Uncertain diagnosis, Bleeding, Enlargement, and Delay in healing." I think it shows just how rare and confusing this disease can be.

Are some people more likely to get acral lentiginous melanoma than others?

Nelson: No. Most melanomas tend to happen in people with light-colored skin. But acral lentiginous melanoma tends to occur at similar rates for people of all different levels of skin color.

So, UV exposure doesn’t really contribute to the development of acral lentiginous melanomas?

Nelson: No. Acral lentiginous melanomas don’t seem to be caused by UV exposure. For one thing, it’s really hard to get a sunburn on the bottom of your feet. And, when we look at studies to try to determine what does cause them, many patients describe a history of trauma to the area involved. 

Glitza: Exactly. You can’t really put sunscreen on your nails or palms or soles. But even if we could, we don’t think UV radiation plays a significant role here. Acral lentiginous melanoma doesn’t have the genetic changes that originate from UV damage. And its genetic makeup is unique. While about half of all skin-based melanomas have a BRAF mutation, the same mutation only appears in about 15% to 20% of acral lentiginous melanomas.

Are there other risk factors people should be aware of?

Glitza: Maybe. Pressure on the feet, whether it’s from wearing high heels or overly tight shoes, could be linked to acral lentiginous melanoma. As Dr. Nelson mentioned, trauma might be a factor, too. Reggae legend Bob Marley, who was an avid soccer player, only learned that he had acral lentiginous melanoma after seeking treatment for a toe injury.

How is acral lentiginous melanoma treated? 

Nelson: In the early stages, we can usually remove it surgically. If it involves a nail, we may be able to use amputation-sparing approaches, so patients don’t have to lose an entire digit.

In more advanced cases, patients may need a lymph node biopsy. Based on the results, we’ll determine the treatment plan. Usually, we’ll offer immunotherapy or targeted therapy, depending on what additional test results show. Since the very first immunotherapy drug developed was made for melanoma, we already have a decade of research to consult for how patients respond to it. However, as acral lentiginous melanoma is rare, only a small number of patients have been included in clinical trials.

Glitza: Even if the none of the therapies above work, we still have other treatment options to offer, such as clinical trials. 

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