Contents
What is acral lentiginous melanoma
Acral lentiginous melanoma is a type of malignant melanoma originating on palms, soles of foot and under the nail. Acral lentiginous melanoma is a form of melanoma characterized by its site of origin: palm, sole, or beneath the nail (subungual melanoma). Acral lentiginous melanoma is more common on feet than on hands. It can arise de novo in normal-appearing skin, or it can develop within an existing melanocytic nevus (mole).
When acral lentiginous melanoma arises in the nail region, it is known as melanoma of the nail unit. If it starts in the matrix (nail growth area), it is called subungual melanoma. It may present as diffuse discoloration or irregular pigmented longitudinal band(s) on the nail plate. Advanced melanoma destroys the nail plate altogether. It can be amelanotic.
Acral lentiginous melanoma starts as a slowly-enlarging flat patch of discolored skin. At first, the malignant cells remain within the tissue of origin, the epidermis. This is the in situ phase of melanoma, which can persist for months or years.
Acral lentiginous melanoma becomes invasive when the melanoma cells cross the basement membrane of the epidermis and malignant cells enter the dermis. A rapidly-growing nodular melanoma can also arise within acral lentiginous melanoma and proliferate more deeply within the skin.
Acral lentiginous melanoma key facts
- Acral lentiginous melanoma cause is unknown.
- Acral lentiginous melanoma is not related to sun exposure
- Acral lentiginous melanoma affects men and women equally
- Acral lentiginous melanoma affects all skin types, and is the most common type of melanoma in dark-skinned patients
- The majority of acral lentiginous melanoma arise in patients over the age of 40
- Acral lentiginous melanomas grow relatively slowly in the early stages, although a reliable history can be difficult, especially for lesions on the soles
- Acral lentiginous melanoma are more common on the soles
- Acral lentiginous melanoma initially present as slow growing deceptively banal-looking pigmented macules or patches, hence the term lentiginous
- The development of nodular areas within the lesion suggests deeper invasion
Figure 1. Acral lentiginous melanoma foot
What is Breslow thickness?
The Breslow thickness is reported for invasive melanomas. It is measured vertically in millimeters from the top of the granular layer (or base of superficial ulceration) to the deepest point of tumor involvement. It is a strong predictor of outcome; the thicker the melanoma, the more likely it is to metastasize (spread).
What is the Clark level of invasion?
The Clark level indicates the anatomic plane of invasion.
- Level 1 — In situ melanoma
- Level 2 — Melanoma has invaded papillary dermis
- Level 3 — Melanoma has filled papillary dermis
- Level 4 — Melanoma has invaded reticular dermis
- Level 5— Melanoma has invaded subcutaneous tissue
The deeper the Clark level, the greater the risk of metastasis (secondary spread). It is useful in predicting outcome in thin tumors, and less useful for thicker ones in comparison to the value of the Breslow thickness.
Who gets acral lentiginous melanoma?
About 1 to 3% of melanomas are acral lentiginous melanoma. Melanoma is a potentially serious skin cancer that arises from pigment cells (melanocytes). Although acral lentiginous melanoma is rare in Caucasians and people with darker skin types, it is the most common subtype in people with darker skins.
Acral lentiginous melanoma is relatively rare compared to other types of melanoma. There is no connection with the colour of skin (skin phototype) and it occurs at equal rates in white, brown or black skin. Acral lentiginous melanoma accounts for 29-72% of melanoma in dark-skinned individuals but less than 1% of melanoma in fair skinned people, as they are prone to more common sun-induced types of melanoma such as superficial spreading melanoma and lentigo maligna melanoma.
Acral lentiginous melanoma is equally common in males and females. The majority arise in people over the age of 40.
The cause or causes of acral lentiginous melanoma are unknown. It is not related to sun exposure.
Acral lentiginous melanoma causes
Acral lentiginous melanoma cause is unknown. Acral lentiginous melanoma is due to the development of malignant pigment cells (melanocytes) along the basal layer of the epidermis. These cells may arise from an existing melanocytic naevus or more often from previously normal-appearing skin. What triggers the melanocytes to become malignant is unknown but it involves genetic mutations.
Acral lentiginous melanoma symptoms
Acral lentiginous melanoma on palm, soles or fingers and toes starts off as an enlarging patch of discolored skin. It is often thought at first to be a stain. It can also be amelanotic (non-pigmented, usually red in color). Like other flat forms of melanoma, it can be recognized by the ABCDE rule: Asymmetry, Border irregularity, Color variation, large Diameter and Evolving.
The characteristics of acral lentiginous melanoma include:
- Large size: >6 mm and often several centimeters or more in diameter at diagnosis
- Variable pigmentation: most often a mixture of brown, and blue-grey, black and red colors
- Smooth surface at first, later becoming thicker with an irregular surface that may be dry or warty
- Ulceration or bleeding
Acral lentiginous melanoma diagnosis
Dermoscopy or the use of a dermatoscope, by a dermatologist or other doctor trained in its use can be very helpful in distinguishing acral lentiginous melanoma from other skin lesions, particularly:
- Melanocytic nevi (moles)
- Viral warts
- Bleeding i.e. subcorneal hemorrhage or subungual haematoma
The most frequently observed dermoscopic features of acral lentiginous melanoma are:
- Asymmetrical structure and colors
- Parallel ridge pattern of pigment distribution
- Blue-grey structures
Biopsy
If the skin lesion is suspicious of acral lentiginous melanoma, it is best cut out (excision biopsy). A partial biopsy is best avoided, except in unusually large lesions. An incisional or punch biopsy could miss a focus of melanoma arising in a pre-existing naevus. However, sometimes the lesion is very large, and before performing significant surgery, a biopsy is arranged to confirm the diagnosis. Biopsy of a lesion suspicious of acral lentiginous melanoma should remove a long ellipse of skin, or there should be several biopsies taken from multiple sites, as a single site could miss a malignant focus.
The pathological diagnosis of melanoma can be very difficult. Histological features of acral lentiginous melanoma includes asymmetric proliferation of melanocytes at the dermoepidermal junction.
Pathology report
The pathologist’s report should include a macroscopic description of the specimen and melanoma (the naked eye view), and a microscopic description.
- Diagnosis of primary melanoma
- Breslow thickness to the nearest 0.1 mm
- Clark level of invasion
- Margins of excision i.e. the normal tissue around the tumor
- Mitotic rate – a measure of how fast the cells are proliferating
- Whether or not there is ulceration
The report may also include comments about the cell type and its growth pattern, invasion of blood vessels or nerves, inflammatory response, regression and whether there is an associated nevus (original mole).
Melanoma Skin Cancer Stages
After someone is diagnosed with melanoma, doctors will try to figure out if it has spread, and if so, how far. This process is called staging. The stage of a cancer describes how much cancer is in the body. It helps determine how serious the cancer is and how best to treat it. Doctors also use a cancer’s stage when talking about survival statistics.
The earliest stage melanomas are called stage 0 (carcinoma in situ), and then range from stages I (1) through IV (4). As a rule, the lower the number, the less the cancer has spread. A higher number, such as stage IV, means cancer has spread more. And within a stage, an earlier letter means a lower stage. Although each person’s cancer experience is unique, cancers with similar stages tend to have a similar outlook and are often treated in much the same way.
The staging system most often used for melanoma is the American Joint Committee on Cancer (AJCC) TNM system, which is based on 3 key pieces of information:
- The extent of the tumor (T): How deep has the cancer grown into the skin? Is the cancer ulcerated?
- Tumor thickness: The thickness of the melanoma is called the Breslow measurement. In general, melanomas less than 1 millimeter (mm) thick (about 1/25 of an inch) have a very small chance of spreading. As the melanoma becomes thicker, it has a greater chance of spreading.
- Ulceration: Ulceration is a breakdown of the skin over the melanoma. Melanomas that are ulcerated tend to have a worse outlook.
- The spread to nearby lymph nodes (N): Has the cancer spread to nearby lymph nodes?
- The spread (metastasis) to distant sites (M): Has the cancer spread to distant lymph nodes or distant organs such as the lungs or brain?
Numbers or letters after T, N, and M provide more details about each of these factors. Higher numbers mean the cancer is more advanced. Once a person’s T, N, and M categories have been determined, this information is combined in a process called stage grouping to assign an overall stage.
The staging system in the table below uses the pathologic stage (also called the surgical stage). It is determined by examining tissue removed during an operation. Sometimes, if surgery is not possible right away or at all, the cancer will be given a clinical stage instead. This is based on the results of a physical exam, biopsy, and imaging tests. The clinical stage will be used to help plan treatment. Sometimes, though, the cancer has spread further than the clinical stage estimates, and may not predict the patient’s outlook as accurately as a pathologic stage.
There are both clinical and pathologic staging systems for melanoma. Since most cancers are staged with the pathologic stage, we have included that staging system below. If your cancer has been clinically staged, it is best to talk to your doctor about your specific stage.
The table below is a simplified version of the TNM system. It is based on the most recent American Joint Committee on Cancer (AJCC) system, effective January 2018. It’s important to know that melanoma cancer staging can be complex. If you have any questions about the stage of your cancer or what it means, please ask your doctor to explain it to you in a way you understand.
Table 1. Melanoma Skin Cancer TNM Stages
| AJCC Stage | Melanoma Stage description | |
| 0 | The cancer is confined to the epidermis, the outermost skin layer. It has not spread to nearby lymph nodes or distant sites. This stage is also known as melanoma in situ. | |
| I
| The cancer is no more than 2mm (2/25 of an inch) thick and might or might not be ulcerated. It has not spread to nearby lymph nodes or to distant sites. | |
| II | The cancer is at least 1.01 mm and may be thicker than 4.0 mm. It might or might not be ulcerated. It has not spread to nearby lymph nodes (N0) or to distant sites (M0).
| |
| IIIA | The cancer is no more than 2.0 mm thick. It might or might not be ulcerated. It has spread to 3 or less lymph node(s), but it is so small that it is only seen under the microscope. It has not spread to distant sites. | |
| IIIB
| There is no sign of the primary cancer AND:
It has not spread to distant sites. | |
| OR | ||
The cancer is no more than 4.0 mm thick. It might or might not be ulcerated AND:
It has not spread to distant sites. | ||
| IIIC | There is no sign of the primary cancer AND:
It has not spread to distant sites. | |
| OR | ||
The cancer is no more than 4.0 mm thick. It might or might not be ulcerated AND:
It has not spread to distant sites. | ||
| OR | ||
The cancer is between 2.1 and 4.0mm OR thicker than 4.0 mm. It might or might not be ulcerated AND:
It has not spread to distant sites. | ||
| OR | ||
The cancer is thicker than 4.0 mm and is ulcerated AND:
It has not spread to distant sites. | ||
| IIID | The cancer is thicker than 4.0 mm and is ulcerated AND:
It has not spread to distant sites. | |
| IV | The cancer can be any thickness and might or might not be ulcerated. It might or might not have spread to nearby lymph nodes. It has spread to distant lymph nodes or organs such as the lungs, liver or brain. | |
Acral lentiginous melanoma treatment
Based on the stage of acral lentiginous melanoma and other factors, your treatment options might include:
- Surgery
- Immunotherapy
- Targeted Therapy
- Chemotherapy
- Radiation Therapy
The initial treatment of a primary melanoma is to cut it out; the lesion should be completely excised with a 2-3 mm margin of normal tissue. Further treatment depends mainly on the Breslow thickness of the lesion.
After initial excision biopsy; the radial excision margins, measured clinically from the edge of the melanoma are shown in the table below. This may necessitate flap or graft to close the wound. In the case of acral lentiginous and subungual melanoma, this may include partial amputation of a digit. Occasionally, the pathologist will report incomplete excision of the melanoma, despite wide margins. This means further surgery or radiotherapy will be recommended to ensure the tumor has been completely removed.
- Melanoma in situ — excision margin 5 mm
- Melanoma < 1.0 mm — excision margin 1 cm
- Melanoma 1.0–2.0 mm — excision margin 1–2 cm
- Melanoma 2.0–4.0 mm — excision margin 1–2 cm
- Melanoma > 4.0 mm — excision margin 2 cm
If melanoma has spread (metastasized) from the skin to other organs such as the lungs or brain, the cancer is very unlikely to be curable by surgery. Even when only 1 or 2 areas of spread are found by imaging tests such as CT or MRI scans, there are likely to be others that are too small to be found by these scans.
Surgery is sometimes done in these circumstances, but the goal is usually to try to control the cancer rather than to cure it. If 1 or even a few metastases are present and can be removed completely, this surgery may help some people live longer. Removing metastases in some places, such as the brain, might also help prevent or relieve symptoms and improve a person’s quality of life.
If you have metastatic melanoma and surgery is a treatment option, talk to your doctor and be sure you understand what the goal of the surgery would be, as well as its possible benefits and risks.
Immunotherapy for melanoma
Immunotherapy is treatment that either boosts your own immune system or uses man-made versions of parts of the immune system that attack the melanoma cells. Many types of immunotherapy are used to treat melanoma. These drugs may be given into a vein, given as a shot, or taken as pills.
Targeted therapy for melanoma
Targeted therapy drugs may be used for certain types of melanoma. These drugs affect mainly cancer cells and not normal cells in the body. They may work even if other treatment doesn’t. They may cause fewer side effects.
Chemotherapy
Chemo is the short word for chemotherapy – the use of drugs to fight cancer. The drugs may be given into a vein or taken as pills. These drugs go into the blood and spread through the body. They kill cells that are fast growing cancer cells and good cells like blood cells and hair. Chemo is given in cycles or rounds. Each round of treatment is followed by a break. Most of the time, 2 or more chemo drugs are given. Treatment often lasts for many months.
Radiation treatments
Radiation uses high-energy rays (like x-rays) to kill cancer cells. Radiation is not usually used to treat the main spot on the skin. But it may be used after surgery to help keep the melanoma from coming back.
Clinical trials
Clinical trials are research studies that test new drugs or other treatments in people. They compare standard treatments with others that may be better.
If you would like to learn more about clinical trials that might be right for you, start by asking your doctor if your clinic or hospital conducts clinical trials.
Clinical trials are one way to get the newest cancer treatment. They are the best way for doctors to find better ways to treat cancer. If your doctor can find one that’s studying the kind of cancer you have, it’s up to you whether to take part. And if you do sign up for a clinical trial, you can always stop at any time.
Acral lentiginous melanoma survival rate
Acral lentiginous melanoma in situ is not dangerous; it only becomes potentially life threatening if an invasive melanoma develops within it. The risk of spread from invasive melanoma depends on several factors, but the main one is the measured thickness of the melanoma at the time it was surgically removed.
The Melanoma Guidelines report that metastases are rare for melanomas <0.75mm and the risk for tumors 0.75–1 mm thick is about 5%. The risk steadily increases with thickness so that melanomas >4 mm; result in a 10-year survival of around 50%, according to the American Joint Committee on Cancer (AJCC) statistics.
Table 2. 5-year relative survival rates for melanoma skin cancer (based on people diagnosed with melanoma between 2008 and 2014)
| SEER stage | 5-year relative survival rate |
| Localized | 98% |
| Regional | 64% |
| Distant | 23% |
| All SEER stages combined | 92% |
Footnote: SEER = Surveillance, Epidemiology, and End Results. The SEER database is maintained by the National Cancer Institute (NCI), to provide survival statistics for different types of cancer.
[Source 2 ]The SEER database tracks 5-year relative survival rates for melanoma skin cancer in the United States, based on how far the cancer has spread. The SEER database, however, does not group cancers by American Joint Committee on Cancer (AJCC) TNM stages (stage 1, stage 2, stage 3, etc.). Instead, it groups cancers into localized, regional, and distant stages:
- Localized: There is no sign that the cancer has spread beyond the skin where it started. This would include AJCC stage 1 and stage 2 cancers.
- Regional: The cancer has spread beyond the skin where it started to nearby structures or lymph nodes. This would include mainly stage 3 cancers in the American Joint Committee on Cancer (AJCC) system.
- Distant: The cancer has spread to distant parts of the body, such as the lungs, liver, or skin on other parts of the body. This would include stage 4 cancers.
- Melanoma Skin Cancer Stages. https://www.cancer.org/cancer/melanoma-skin-cancer/detection-diagnosis-staging/melanoma-skin-cancer-stages.html[↩]
- Survival Rates for Melanoma Skin Cancer. https://www.cancer.org/cancer/melanoma-skin-cancer/detection-diagnosis-staging/survival-rates-for-melanoma-skin-cancer-by-stage.html[↩]
