Acral lentiginous melanoma is a type of melanoma arising on the palms or soles of the feet. Acral lentiginous melanoma is not just a fancy name for melanoma on the fingers, toes, palm, soles of the feet, and under the nails, but it is also a type of melanoma that is the rarest among melanomas, accounting for only 2% to 3% of melanoma cases. Acral lentiginous melanoma is seen more common in white skinned people compared to the dark skin ones. It is more common on the feet than on the hands, and it can arise on normal-appearing skin, or it can develop within an existing melanocytic naevus (mole).
Melanoma can also develop on the mucous membranes of the anus, urinary tract and female genitalia. The mucous membranes are specialized areas of skin which have a unique lining. The early symptoms of melanoma present in these places are bleeding of the nose, nasal stuffiness or a mass which is pigmented inside the mouth.
There is no direct connection with the colour of the skin and it occurs at the same rates in white, brown or black skin. The acral lentiginous melanoma accounts for 29 to 72 percent of melanoma in dark skinned individuals. it is less than one percent of melanoma in people with fair skin since they are more prone to common sun-induced types of melanoma such as lentigo maligna melanoma.
Melanoma is a potentially serious skin cancer that arises from pigment cells (melanocytes). Like cutaneous malignant melanoma, which is doctor-speak for ordinary melanoma, acral lentiginous melanoma progresses rapidly and leads to death if not treated. However, the two have interesting differences. Aside from arising from the skin of the hands or feet, acral lentiginous melanoma tends to afflict people with black or brown skin color. Meanwhile, ordinary melanoma tends to afflict individuals with pale or fair skin complexion. Acral lentiginous melanoma can be deadly. The exact cause of acral lentiginous melanoma is not fully understood, and it is not associated with sun exposure like ordinary melanoma. Here is what you must know about this type of melanoma.
The specific cause of acral lentiginous melanoma is still unknown. It is thought that the melanoma develops when there are problems with the DNA. These DNA controls certain skin cells. People affected with acral lentiginous melanoma have damaged DNA which causes an overgrowth of the skin cells that produce skin pigment. It becomes cancerous melanoma growth when there is overproduction of these cells. Older people are at risk of getting acral lentiginous melanoma. If there has been a family history of melanoma you are at a higher risk for the disease.
What does it look like?
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 continue for months or sometimes even years. At first, acral lentiginous melanoma often appears as an innocuous streak, patch, or "stain" of discolored skin on the fingers, toes, palms, soles of the feet, or under the fingernails. Some cases have red-colored patches or streaks. Sometimes, the lesion may appear in the mouth or inside the nose. If it appears inside the nose, the patient may experience frequent nosebleeds or stuffiness. It is often large size which is more than 6mm and often several centimeters or more in diameter at diagnosis.
The lesion enlarges slowly, may have open wounds, or may bleed over time.
Like ordinary melanoma, acral lentiginous melanoma lesions often exhibit one or more of the ABCDE rule:
- A – Asymmetry. One half of the lesion does not match the other half when divided into two.
- B – Border irregularity. The edges of the lesion are often blurred or poorly-defined.
- C – Color. Most lesions have noticeable color variation. Acral lentiginous melanoma lesions tend to have a mix of brown, blue-gray, black, or red in color.
- D – Diameter. Be alarmed if the lesion is larger than a pencil eraser, because it could be cancerous.
- E – Evolving. Acral lentiginous melanoma tends to change. From having a smooth surface, the lesion gradually becomes thicker, drier, or more warty.
When it appears under the nails, acral lentiginous melanoma first appears as a diffuse discoloration or vividly colored bands on the nails. The affected nail may lift up or separate from the nail bed due to the lesion. Over time, the lesion grows and disfigures the nail bed. Since acral lentiginous melanoma often occurs in individuals with brown or black skin, and it may grow in relatively hidden areas, like under the nails or soles of the feet. Suspicious patches or streaks are often unnoticed. 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.
Cause of acral lentiginous melanoma
The exact cause of acral lentiginous melanoma is still unknown. However, it is due to the development of malignant pigment cells also called as melanocytes along with the basal layer of the epidermis. These cells can arise from an existing melanocytic naevus or often from previous skin which was appearing as normal. The question of what triggers the melanocytes to become so dangerous is still unknown but there is involvement of genetic mutation.
Some of the warning signs are new areas of pigmentation or any existing pigmentation that shows changes. This usually occurs at the membrane of the outer layers of the skin.
Types of melanoma in the foot
There are four types of melanoma arising in the foot: nodular, superficial spreading, subungual melanomas and the last but the most common is acral lentiginous melanoma. The lesions due to acral are not only on the foot. They include soles, palms, volar surfaces of fingers and toes.
A doctor should check for any unusual patches or streaks on the skin. Acral lentiginous melanoma is often mistaken as a bruise; note that bruises fade in few days. A whole-body skin check done by a dermatologist can easily determine the presence of moles or suspicious skin lesions. The doctor usually uses an instrument called a dermatoscope to closely examine lesions.
If any of them look suspicious, the doctor may order a biopsy of the lesion. A biopsy removes a part of a large lesion, or totally removes it if it is small enough, and has it examined in the laboratory for the presence of cancerous cells. The most frequently observed dermoscopic features of acral lentiginous melanoma are asymmetrical structure, abonormal color, and a parallel ridge pattern of pigment distribution along with blue-grey structures on the affected area.
Dermoscopy of acral lesion is an important tool for diagnosis and management of the plantar pigmented lesion. It is a non-invasive technique which facilitates accurate screening examination of the skin. It provides up to ten times the magnification of the skin lesion.
During diagnosis, a doctor checks the following to determine if it is cancerous:
- Depth of the lesion
- Thickness of the lesion
- Presence of ulceration
- Margins of the lesion
- The mitotic rate, or the measure on how fast cells are dividing. Unusually rapid cell division is a hallmark of cancer
If the lesion is found to be cancerous and has invaded tissues deep below the skin, the doctor may check nearby lymph nodes as well.
Pathology report – the report from the pathologists includes a macroscopic detail of the specimen and melanoma along with a microscopic description:
- Clark level of invasion
- Primary melanoma diagnosis
- The tissue around the tumor
- Whether there is any ulceration
- Measuring how fast the cells are proliferating
- Inflammatory response
- Whether there is any associated naevus
- Type of cell and its growth pattern
It has been demonstrated that acral lentiginous melanoma has a poorer prognosis rate in comparison to cutaneous malignant melanoma (CMM). This may be because it affects people with dark or brown skin, and lesions often stay relatively hidden. Thus, many patients seek treatment when cancerous lesions have worsened and have spread to other parts of the body. In most cases, only a small percentage of patients with acral lentiginous melanoma survives within 3 years of the diagnosis. As with ordinary melanoma, early detection and treatment of acral lentiginous melanoma increase chances of successful treatment.
The treatment of a primary melanoma is to cut the lesion. The lesion should be completely excised with a 2 – 3 mm margin of normal tissue.
Surgery is still the mainstay of treatment, as there are no proven effective systemic treatments. Although several reliable national guidelines for melanoma have been formed using the evidence-based method, there are still some controversies in the treatment of the disease. Because of the biological and unique anatomical specificity of ALM, it is still unclear whether or not the thickness of ALM and recommended lateral margins are the same as that of other subtypes. Acral lentiginous melanoma can therefore be removed by surgery and treated with radiation or chemotherapy. If cancer has spread to the lymph nodes, the doctor may remove them as well. Acral lentiginous melanoma is more difficult to treat if the primary tumor becomes invasive, because it then spreads cancerous cells to other parts of the body. Along with the removal of the primary tumor with surgery, radiation or chemotherapy is used to kill cancerous cells in other organs.
Melanoma Staging – This relates to find out if the melanoma has spread from its original site in the skin. There are different stages:
- Stage 0 – in situ melanoma
- Stage 1 – thin melanoma with thickness of less than 2mm
- Stage 2 – thick melanoma with thickness of more than 2mm
- Stage 3 – the local lymph nodes also get involved due to the spreading of melanoma
- Stage 4 – distant metastases is detected
Due to metastatic melanoma if the local lymph nodes get enlarged then they should be removed completely. The doctor would perform surgical procedure to get it removed usually under general anesthetic. However, if they are not enlarged then it would be tested to see if there is any microscopic spread of melanoma. This test is known as sentinel node biopsy. If the lymph nodes contain metastatic melanoma, then it often increases in size quickly.
Other forms of treatment would be required if there is widespread of melanoma in the body. But not all the treatments are completely successful in fully eradicating cancer.
Follow-up with the doctor
To avoid recurrences one should ensure to have follow-ups with the doctor.
- Self-skin examination
- Ensure regular routine skin checkup.
- The doctor would check the scar where primary melanoma was removed.
- They would also do a check to feel if there is no presence of regional lymph nodes.
- For patients with more serious conditions the doctor would recommend blood tests, X-ray, ultrasound, MRI or Imaging.
Is acral melanoma lethal
An acral lentiginous melanoma appears as dark in colour. At times its brown or black, unevenly pigmented patch. If the lesion becomes raised, then there is likelihood of invasion which is much higher. Some tumors may appear as flat which may have invaded along the perieccrine adventitial dermis but one may never know if it has penetrated deeper to the subcutaneous adipose tissue. One of the reasons for acral melanoma being lethal is that prognostic difference may be the general omission of the feet from general physical examination. As you age the risk factor also increases. At times there are chances of misdiagnosis. Patients are less likely to completely examine themselves. Even if the abnormality is noticed but often the diagnosis is not done correctly.
Does sun exposure increase the risk of acral lentiginous melanoma?
Unlike other types of melanoma, acral lentiginous melanoma is not related to sun exposure. It develops on the areas of the skin that are not exposed to the sun such as palms, soles, nail beds or mucous membranes. Acral begins in the same type of cell that produces the pigment which causes sun to tan when it is exposed to the sun. However, these cells are found all over the skin and not just in areas exposed to the sun.
Acral lentiginous melanoma is a very sever form of skin cancer, and it should be treated as quickly as possible for the best results. It gets life threatening if there is any development of invasive melanoma. Be sure to visit a doctor such as a dermatologist if you notice any abnormalities on the skin.