What is Acral Lentiginous Melanoma?
Acral lentiginous melanoma, or simply acral melanoma, is a type of skin cancer that occurs on the extremities of the body, like the palms, soles, fingers, toes, and around the nails. The term ‘acral’ comes from a Greek word that refers to the highest or topmost portions of the limbs. ‘Lentiginous’ describes how these tumors initially appear as a flat, brown spot, much like a harmless skin mark called a lentigo.
Melanoma is the medical name for cancer of the melanocytes, which are the cells in your skin that produce pigment. Acral melanoma was first identified as a unique type of skin cancer in 1977. It is the least common type of melanoma, making up just 2 to 3% of all melanoma diagnoses. Unlike other types of skin cancer, sun exposure doesn’t seem to be a major cause of acral melanoma.
Acral melanoma most often occurs on the lower limbs, and because it is often detected late, it has a high mortality rate. Interestingly, compared to other types of melanoma, acral melanoma is more commonly found in non-white populations. This document will discuss the unique aspects of this disease.
What Causes Acral Lentiginous Melanoma?
Several studies suggest that stress or pressure might contribute to the development of Acral Lentiginous Melanoma (ALM), as this type of skin cancer is more common in areas of the foot that bear weight, like the heel, front, and side of the foot. Melanoma on the foot’s arch is less common but appears to occur more frequently in people with obesity.
However, recent findings show that when accounting for the foot’s surface area, there seems to be an inverse relationship between ALM and unusual or benign skin growths in areas that bear weight. Also, ALM appears to occur more often on the soles of the feet compared to the palms of the hands, possibly because the soles have 50% more melanocytes, the cells where this cancer starts, compared to the palms.
Research also indicates that injuries that break the skin might increase the risk of ALM compared to people without such injuries. Interestingly, the typical genetic changes seen in other types of Cutaneous Malignant Melanoma (CMM) that are linked to UV exposure aren’t found in ALM. The exact cause of ALM is still not fully understood, but research suggests that genetic factors may play a role.
Risk Factors and Frequency for Acral Lentiginous Melanoma
ALM, or Acral Lentiginous Melanoma, accounts for 2 to 3% of all new melanoma cases. People are typically diagnosed with ALM around the age of 62.8, with the number of cases increasing as people get older. There’s a notable spike in the number of cases among people over 80.
ALM affects both men and women equally, but women are often diagnosed at an earlier stage than men. This type of melanoma is more common in non-white individuals compared to other types, although it is not the most common type in any racial group in the United States. However, in Mexico, Taiwan, and China, ALM is the most common subtype.
- In the black population in the US, ALM makes up 33-36% of all melanoma cases.
- For Asian/Pacific Islanders in the US, ALM represents 18-23.1% of all melanoma cases.
- In Hispanic Whites, ALM makes up 9% of melanoma cases and only 1% in non-Hispanic whites.
- The rate of ALM cases is highest among Hispanic Whites, at 2.5 per 1,000,000 people per year, and lower in Blacks, Non-Hispanic Whites, and Asian/Pacific Islanders at 1.8, 1.8, and 1.1 per 1,000,000 people per year, respectively.
The survival rate from melanoma is generally lower in Black and Hispanic White populations at 5 and 10 years compared to whites. However, when adjusting for the severity of the disease at the time of diagnosis, there’s no difference in survival rates. This highlights how important it is to catch the disease early, particularly in minority groups.
Signs and Symptoms of Acral Lentiginous Melanoma
Acral Lentiginous Melanoma (ALM) is a skin condition that typically starts as a light to dark brown spot. It usually has sharp edges. In time, it may become a bumpy and dark mass, its color changing from blue to black. The mass might even develop ulcers as it further develops.
Physicians use a simplified acronym “CUBED” to identify melanoma on the skin’s acral surfaces, which includes
- Colored lesions that have various shades
- Uncertain diagnosis, i.e., unclear skin condition
- Bleeding lesions
- Enlargement of a lesion
- Delay in healing that goes beyond two months
Dermoscopy, a method to examine the skin, is a helpful tool to identify worrying pigment patterns in acral lesions. Two system proposals have been made to examine pigmented acral lesions using dermoscopy. The first one, proposed by Koga and Saida, looks at a three-step algorithm that checks certain features in the acral lesion. The second one, proposed by Lallas and others, uses an acronym ‘BRAFF’ with six dermatoscopic indications.
However, it is highly recommended to biopsy skin lesions with a diameter more than 7 mm due to the potential risk of melanoma. Furthermore, lesions larger than 9mm are likely to be melanoma.
ALM of the nail often appears as diffuse pigmentation, pigmented striping of the nail, or other non-pigmented transformations such as ulcers. If the pigmentation from an ALM under the nail expands into the nail fold, known as the Hutchinson sign, it could be a concerning sign. Initially, the lesion might only result in pigmentation changes to the nail fold, but in advanced cases, it may extend into the neighboring smooth skin.
Testing for Acral Lentiginous Melanoma
If there are signs pointing to skin cancer, particularly melanoma, a procedure called a narrow margin excisional biopsy is usually suggested. This involves removing a small section around the suspected area. However, doing such a procedure can be tricky in certain parts of the body like hands and feet. When this is the case, only taking a sample of the initial area is considered an acceptable alternative. The risk here is that partial samples might not give an accurate diagnosis.
When a spot on the nail looks suspicious, a sample of the nail matrix (the area where the nail starts growing) is needed. This can be a bit complex and must be done by a medical professional who is especially skilled in this type of procedure to ensure an accurate diagnosis. Often, a medical expert who specializes in skin pathology, known as a dermatopathologist, may also be needed to interpret the results accurately.
If skin cancer has been detected early and hasn’t spread and the patient doesn’t have any other symptoms, additional tests or scans usually aren’t needed. In later stages of melanoma, measurements of lactate dehydrogenase levels in the blood can help predict how the patient will fare, especially for those with stage IV (advanced) disease.
Radiology tests to check whether the cancer has spread can often lead to false alarms, suggesting that cancer is present when it isn’t. But if such tests are obtained, a simple chest x-ray is often seen as a cost-effective method. Likely, getting unnecessary tests may lead to unwanted invasive procedures. It’s usually enough to have a yearly skin check and palpation of regional lymph nodes (feeling the nearby nodes for any abnormalities) to look for any signs of cancer coming back.
The procedure known as sentinel lymph node biopsy, where the lymph node that is the first to receive cancer cells is removed and examined, can provide significant information about the prognosis for those with intermediate and severe forms of melanoma. For patients with intermediate severity melanomas and sentinel lymph node metastases, undergoing this biopsy procedure and complete removal of the lymph nodes significantly improved survival rate – 62.1% versus only 41.5% in the group only observed. However, for patients with severe melanomas, the biopsy procedure did not make much difference to survival rates. Nevertheless, there is some controversy around these findings, with some experts questioning the true survival benefit of sentinel lymph node biopsies.
Treatment Options for Acral Lentiginous Melanoma
The principal treatment for ALM (a type of skin cancer) is a surgical procedure known as wide local excisions. The exact surgical boundaries depend on how thick the tumor is at the time of the biopsy, as discussed in more depth in the surgical oncology section. Sometimes, if surgery isn’t suitable, it might be possible to avoid surgical removal of pre-cancerous lesions.
Topical imiquimod, a skin cream, has been studied as an alternative treatment, but it’s not officially recommended for this purpose. There are several potential downsides. For example, pre-cancerous lesions may persist, invasive lesions may go undetected because there’s no surgery, and the treatment can be expensive. And the lesions might even progress.
If the cancer has spread – either noticeably or as revealed by feeling local lymph nodes or a sentinel lymph node biopsy – systemic treatment might be necessary. This could involve chemotherapy, targeted mutation therapy, or immune checkpoint inhibitors, which are detailed further in the oncology section. However, no survival benefit has been observed in treating patients who show no symptoms of advanced stage disease before symptoms start.
What else can Acral Lentiginous Melanoma be?
When trying to diagnose ALM (a type of skin cancer), there are numerous other conditions that need to be ruled out. These include other forms of skin cancer, such as lentigo, congenital acral nevi, and acquired acral nevi. If the ALM is present under the nail (subungual), potential diagnoses could be ethnic pigmentation, lentigo, or nevi.
There are also several non-cancerous conditions that share symptoms with ALM. These conditions present on smooth skin (glabrous) and under the nails, and include bacterial and fungal infections, injury-related bleeding (talon noir), a certain skin condition (terra firma-forme dermatosis), long-lasting wounds, verrucae, and other types of skin cancer like squamous cell carcinoma or porocarcinoma, which can be pigmented too. It’s essential to carefully examine symptoms and conduct necessary tests to achieve an accurate diagnosis.
Surgical Treatment of Acral Lentiginous Melanoma
The main treatment for acral lentiginous melanoma, or ALM, is a procedure called wide local excision. This means removing the cancerous cells along with some healthy tissue for good measure.
The exact amount of healthy tissue that should be removed depends on something called the Breslow depth, which is a measure of how deep the melanoma has grown. The rules of thumb are:
- If the melanoma is only skin-deep (referred to as ‘in-situ lesions’), doctors try to remove 0.5 to 1 cm of healthy tissue around it.
- If the melanoma is less than 1 mm deep, they aim for 1 cm of healthy tissue.
- If the melanoma is between 1.01 and 2 mm deep, then 1 to 2 cm of healthy tissue is recommended.
- If the melanoma is deeper than 2 mm, they aim to remove around 2 cm of healthy tissue.
After the procedure, the hole left by the excision can be difficult to close especially if it’s large and located on a part like a finger or a toe. This might require a skin graft or a flap reconstruction, which uses skin from another part of your body to cover the wound. Going for a primary closure, or closing the wound straight away, is typically preferred because it’s generally faster, has fewer complications, and is less expensive.
However, if the wound left by the excision is larger than 1.5 cm, alternatives to primary closure might be needed to avoid painful scars and tightened (or contracted) skin. For melanomas located on fingers and toes, excising the melanoma widely has been found to produce the same prognosis as full amputations.
Melanomas under the nail are challenging to remove due to their proximity to the bone. Traditionally, the treatment option was amputation of the digit. However, recent studies on conservative surgical excision (removing the tumor widely without removing any bone) followed by a full-thickness skin graft showed better outcomes in terms of functionality and appearance, without compromising on disease-free survival. Now, a large-scale study is ongoing to confirm these findings.
What to expect with Acral Lentiginous Melanoma
The prognosis, or likely outcome, for Acral Lentiginous Melanoma (ALM) is determined by several factors. These include aspects like gender, race, age, the depth of tumor penetration in the skin, presence of ulcers, stage of the disease, and whether cancer cells are found in the sentinel lymph nodes (the first nodes cancer is likely to spread to).
In two separate studies, the most significant indicator of disease return and death from melanoma was found to be the presence of positive sentinel lymph nodes.
Compared to other types of melanoma at the same stage and depth, ALM tends to have lower survival rates. However, a few studies suggest that the survival rates could be similar. ALM often presents at a more advanced stage for a variety of reasons. These can include factors like the difficulty older people might face in observing their feet’s soles, not being aware of the risk of melanoma in certain populations, lack of access to healthcare, and other cultural factors.
Possible Complications When Diagnosed with Acral Lentiginous Melanoma
Large-scale removal of ALM, particularly on the hands, can lead to tightening of skin and painful scars, which can cause a lot of health problems. If removal of a finger or an entire limb is necessary for treatment, people can have a considerable disturbance in their daily activities. These disturbances can include the following:
- Loss of function of the affected limb
- Fake sensations of pain from the removed limb (phantom pain)
- Unsatisfactory cosmetic outcomes
Preventing Acral Lentiginous Melanoma
Since we can’t pinpoint exactly what causes ALM (a type of skin cancer), it’s hard to know how to prevent it. The best approach to dealing with ALM is to educate patients and catch the disease early. This can significantly improve a patient’s chances of surviving the disease. People who aren’t often exposed to the sun, such as some ethnic groups, need more education about this disease. This is because they have a lower survival rate compared to non-Hispanic White groups and might not know the warning signs of melanoma, a type of skin cancer.
